diff --git a/akka-stream-tests/src/test/resources/reference.conf b/akka-stream-tests/src/test/resources/reference.conf
index ffbc14a271..107a9f2c70 100644
--- a/akka-stream-tests/src/test/resources/reference.conf
+++ b/akka-stream-tests/src/test/resources/reference.conf
@@ -8,4 +8,5 @@ akka {
   akka.actor.warn-about-java-serializer-usage = false
 
   stream.materializer.debug.fuzzing-mode = on
+  stream.secret-test-fuzzing-warning-disable = 42
 }
\ No newline at end of file
diff --git a/akka-stream-tests/src/test/scala/akka/stream/impl/fusing/InterpreterSpec.scala b/akka-stream-tests/src/test/scala/akka/stream/impl/fusing/InterpreterSpec.scala
index da05c2e2c4..4e68f3b3cd 100644
--- a/akka-stream-tests/src/test/scala/akka/stream/impl/fusing/InterpreterSpec.scala
+++ b/akka-stream-tests/src/test/scala/akka/stream/impl/fusing/InterpreterSpec.scala
@@ -511,7 +511,9 @@ class InterpreterSpec extends AkkaSpec with GraphInterpreterSpecKit {
       downstream.requestOne()
       lastEvents() should be(Set(RequestOne))
 
-      upstream.onComplete()
+      EventFilter[IllegalArgumentException](pattern = ".*Cannot pull closed port.*", occurrences = 1).intercept {
+        upstream.onComplete()
+      }
       val ev = lastEvents()
       ev.nonEmpty should be(true)
       ev.forall {
diff --git a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowIteratorSpec.scala b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowIteratorSpec.scala
index 75ade88c1b..ad94d7d3e5 100644
--- a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowIteratorSpec.scala
+++ b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowIteratorSpec.scala
@@ -4,7 +4,6 @@
 package akka.stream.scaladsl
 
 import akka.NotUsed
-
 import scala.collection.immutable
 import scala.concurrent.duration._
 import akka.stream.ActorMaterializer
@@ -14,6 +13,7 @@ import akka.stream.testkit.Utils._
 import org.reactivestreams.Subscription
 import akka.testkit.TestProbe
 import org.reactivestreams.Subscriber
+import akka.testkit.EventFilter
 
 class FlowIteratorSpec extends AbstractFlowIteratorSpec {
   override def testName = "A Flow based on an iterator producing function"
@@ -40,7 +40,9 @@ class FlowIterableSpec extends AbstractFlowIteratorSpec {
     sub.request(1)
     c.expectNext(1)
     c.expectNoMsg(100.millis)
-    sub.request(2)
+    EventFilter[IllegalStateException](message = "not two", occurrences = 1).intercept {
+      sub.request(2)
+    }
     c.expectError().getMessage should be("not two")
     sub.request(2)
     c.expectNoMsg(100.millis)
diff --git a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowZipWithSpec.scala b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowZipWithSpec.scala
index 6dd7130d00..b2df91f174 100644
--- a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowZipWithSpec.scala
+++ b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/FlowZipWithSpec.scala
@@ -6,6 +6,7 @@ package akka.stream.scaladsl
 import akka.stream.testkit.{ BaseTwoStreamsSetup, TestSubscriber }
 import org.reactivestreams.Publisher
 import scala.concurrent.duration._
+import akka.testkit.EventFilter
 
 class FlowZipWithSpec extends BaseTwoStreamsSetup {
 
@@ -46,7 +47,9 @@ class FlowZipWithSpec extends BaseTwoStreamsSetup {
       probe.expectNext(1 / -2)
       probe.expectNext(2 / -1)
 
-      subscription.request(2)
+      EventFilter[ArithmeticException](occurrences = 1).intercept {
+        subscription.request(2)
+      }
       probe.expectError() match {
         case a: java.lang.ArithmeticException ⇒ a.getMessage should be("/ by zero")
       }
diff --git a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/GraphUnzipWithSpec.scala b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/GraphUnzipWithSpec.scala
index bca40a7173..1c778547a4 100644
--- a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/GraphUnzipWithSpec.scala
+++ b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/GraphUnzipWithSpec.scala
@@ -8,9 +8,9 @@ import akka.stream.testkit.TestSubscriber.Probe
 import akka.stream.testkit.Utils._
 import akka.stream.testkit._
 import org.reactivestreams.Publisher
-
 import scala.concurrent.duration._
 import scala.util.control.NoStackTrace
+import akka.testkit.EventFilter
 
 class GraphUnzipWithSpec extends AkkaSpec {
 
@@ -174,7 +174,9 @@ class GraphUnzipWithSpec extends AkkaSpec {
       leftProbe.expectNext(1 / -1)
       rightProbe.expectNext("1/-1")
 
-      requestFromBoth()
+      EventFilter[ArithmeticException](occurrences = 1).intercept {
+        requestFromBoth()
+      }
 
       leftProbe.expectError() match {
         case a: java.lang.ArithmeticException ⇒ a.getMessage should be("/ by zero")
diff --git a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/GraphZipWithSpec.scala b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/GraphZipWithSpec.scala
index af77a0f652..bda0179180 100644
--- a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/GraphZipWithSpec.scala
+++ b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/GraphZipWithSpec.scala
@@ -3,6 +3,7 @@ package akka.stream.scaladsl
 import akka.stream.testkit._
 import scala.concurrent.duration._
 import akka.stream._
+import akka.testkit.EventFilter
 
 class GraphZipWithSpec extends TwoStreamsSetup {
   import GraphDSL.Implicits._
@@ -65,7 +66,9 @@ class GraphZipWithSpec extends TwoStreamsSetup {
       probe.expectNext(1 / -2)
       probe.expectNext(2 / -1)
 
-      subscription.request(2)
+      EventFilter[ArithmeticException](occurrences = 1).intercept {
+        subscription.request(2)
+      }
       probe.expectError() match {
         case a: java.lang.ArithmeticException ⇒ a.getMessage should be("/ by zero")
       }
diff --git a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/SourceSpec.scala b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/SourceSpec.scala
index 257160b049..0655f1d248 100644
--- a/akka-stream-tests/src/test/scala/akka/stream/scaladsl/SourceSpec.scala
+++ b/akka-stream-tests/src/test/scala/akka/stream/scaladsl/SourceSpec.scala
@@ -13,6 +13,7 @@ import scala.util.control.NoStackTrace
 import akka.stream._
 import akka.stream.testkit._
 import akka.NotUsed
+import akka.testkit.EventFilter
 
 class SourceSpec extends AkkaSpec with DefaultTimeout with ScalaFutures {
 
@@ -235,13 +236,14 @@ class SourceSpec extends AkkaSpec with DefaultTimeout with ScalaFutures {
 
     "terminate with a failure if there is an exception thrown" in {
       val t = new RuntimeException("expected")
-      whenReady(
-        Source.unfold((0, 1)) {
-          case (a, _) if a > 10000000 ⇒ throw t
-          case (a, b)                 ⇒ Some((b, a + b) → a)
-        }.runFold(List.empty[Int]) { case (xs, x) ⇒ x :: xs }.failed) {
-          _ should be theSameInstanceAs (t)
-        }
+      EventFilter[RuntimeException](message = "expected", occurrences = 1) intercept
+        whenReady(
+          Source.unfold((0, 1)) {
+            case (a, _) if a > 10000000 ⇒ throw t
+            case (a, b)                 ⇒ Some((b, a + b) → a)
+          }.runFold(List.empty[Int]) { case (xs, x) ⇒ x :: xs }.failed) {
+            _ should be theSameInstanceAs (t)
+          }
     }
 
     "generate a finite fibonacci sequence asynchronously" in {
diff --git a/akka-stream/src/main/boilerplate/akka/stream/scaladsl/GraphApply.scala.template b/akka-stream/src/main/boilerplate/akka/stream/scaladsl/GraphApply.scala.template
index 6af4c5ea84..c7aa13a5b3 100644
--- a/akka-stream/src/main/boilerplate/akka/stream/scaladsl/GraphApply.scala.template
+++ b/akka-stream/src/main/boilerplate/akka/stream/scaladsl/GraphApply.scala.template
@@ -15,7 +15,7 @@ trait GraphApply {
   def create[S <: Shape]()(buildBlock: GraphDSL.Builder[NotUsed] ⇒ S): Graph[S, NotUsed] = {
     val builder = new GraphDSL.Builder
     val s = buildBlock(builder)
-    val mod = builder.module.nest().replaceShape(s)
+    val mod = builder.module.replaceShape(s)
 
     new GraphApply.GraphImpl(s, mod)
   }
@@ -28,7 +28,7 @@ trait GraphApply {
     val builder = new GraphDSL.Builder
     val s1 = builder.add(g1)
     val s = buildBlock(builder)(s1)
-    val mod = builder.module.nest().replaceShape(s)
+    val mod = builder.module.replaceShape(s)
 
     new GraphApply.GraphImpl(s, mod)
   }
@@ -47,7 +47,7 @@ trait GraphApply {
     [2..#val s1 = builder.add(g1, (f: M1 ⇒ Any, m1: M1) ⇒ f(m1))#
     ]
     val s = buildBlock(builder)([#s1#])
-    val mod = builder.module.nest().replaceShape(s)
+    val mod = builder.module.replaceShape(s)
 
     new GraphApply.GraphImpl(s, mod)
   }#
@@ -63,7 +63,7 @@ private[stream] object GraphApply {
     extends Graph[S, Mat] {
 
     override def withAttributes(attr: Attributes): Graph[S, Mat] =
-      new GraphImpl(shape, module.withAttributes(attr).nest())
+      new GraphImpl(shape, module.withAttributes(attr))
 
     override def named(name: String): Graph[S, Mat] = withAttributes(Attributes.name(name))
   }
diff --git a/akka-stream/src/main/scala/akka/stream/impl/ActorMaterializerImpl.scala b/akka-stream/src/main/scala/akka/stream/impl/ActorMaterializerImpl.scala
index db581e1860..2d6ee38d94 100644
--- a/akka-stream/src/main/scala/akka/stream/impl/ActorMaterializerImpl.scala
+++ b/akka-stream/src/main/scala/akka/stream/impl/ActorMaterializerImpl.scala
@@ -36,7 +36,7 @@ private[akka] case class ActorMaterializerImpl(system: ActorSystem,
   private val _logger = Logging.getLogger(system, this)
   override def logger = _logger
 
-  if (settings.fuzzingMode) {
+  if (settings.fuzzingMode && !system.settings.config.hasPath("akka.stream.secret-test-fuzzing-warning-disable")) {
     _logger.warning("Fuzzing mode is enabled on this system. If you see this warning on your production system then " +
       "set akka.stream.materializer.debug.fuzzing-mode to off.")
   }
diff --git a/akka-stream/src/main/scala/akka/stream/impl/StreamLayout.scala b/akka-stream/src/main/scala/akka/stream/impl/StreamLayout.scala
index 3c52cd29ee..4e4bf7393a 100644
--- a/akka-stream/src/main/scala/akka/stream/impl/StreamLayout.scala
+++ b/akka-stream/src/main/scala/akka/stream/impl/StreamLayout.scala
@@ -136,6 +136,10 @@ object StreamLayout {
     /**
      * Verify that the given Shape has the same ports and return a new module with that shape.
      * Concrete implementations may throw UnsupportedOperationException where applicable.
+     *
+     * Please note that this method MUST NOT be implemented using a CopiedModule since
+     * the purpose of replaceShape can also be to rearrange the ports (as in BidiFlow.reversed)
+     * and that purpose would be defeated.
      */
     def replaceShape(s: Shape): Module
 
@@ -199,7 +203,7 @@ object StreamLayout {
         downstreams.updated(from, to),
         upstreams.updated(to, from),
         materializedValueComputation,
-        attributes)
+        if (isSealed) Attributes.none else attributes)
     }
 
     final def transformMaterializedValue(f: Any ⇒ Any): Module = {
@@ -289,39 +293,20 @@ object StreamLayout {
         Attributes.none)
     }
 
-    /**
-     * Creates a new Module which contains `this` Module
-     * @return a new Module
-     */
-    def nest(): Module = {
-      if (Debug) validate(this)
-
-      CompositeModule(
-        Set(this),
-        shape,
-        /*
-         * Composite modules always maintain the flattened upstreams/downstreams map (i.e. they contain all the
-         * layout information of all the nested modules). Copied modules break the nesting, scoping them to the
-         * copied module. The MaterializerSession will take care of propagating the necessary Publishers and Subscribers
-         * from the enclosed scope to the outer scope.
-         */
-        downstreams,
-        upstreams,
-        /*
-         * Wrapping like this shields the outer module from the details of the
-         * materialized value computation of its submodules.
-         */
-        Atomic(this),
-        Attributes.none)
-    }
-
     def subModules: Set[Module]
-    final def isSealed: Boolean = isAtomic || isCopied || isFused
+    final def isSealed: Boolean = isAtomic || isCopied || isFused || attributes.attributeList.nonEmpty
 
     def downstreams: Map[OutPort, InPort] = Map.empty
     def upstreams: Map[InPort, OutPort] = Map.empty
 
     def materializedValueComputation: MaterializedValueNode = Atomic(this)
+
+    /**
+     * The purpose of this method is to create a copy to be included in a larger
+     * graph such that port identity clashes are avoided. Where a full copy is not
+     * possible or desirable, use a CopiedModule. The shape of the resulting
+     * module MUST NOT contain the same ports as this module’s shape.
+     */
     def carbonCopy: Module
 
     def attributes: Attributes
@@ -342,8 +327,6 @@ object StreamLayout {
     override def compose[A, B, C](that: Module, f: (A, B) ⇒ C): Module =
       throw new UnsupportedOperationException("It is invalid to combine materialized value with EmptyModule")
 
-    override def nest(): Module = this
-
     override def subModules: Set[Module] = Set.empty
 
     override def withAttributes(attributes: Attributes): Module =
@@ -368,7 +351,7 @@ object StreamLayout {
 
     override def replaceShape(s: Shape): Module = {
       shape.requireSamePortsAs(s)
-      copy(shape = s)
+      CompositeModule(this, s)
     }
 
     override val materializedValueComputation: MaterializedValueNode = Atomic(copyOf)
@@ -379,12 +362,12 @@ object StreamLayout {
   }
 
   final case class CompositeModule(
-    override val subModules: Set[Module],
-    override val shape: Shape,
-    override val downstreams: Map[OutPort, InPort],
-    override val upstreams: Map[InPort, OutPort],
-    override val materializedValueComputation: MaterializedValueNode,
-    override val attributes: Attributes) extends Module {
+      override val subModules: Set[Module],
+      override val shape: Shape,
+      override val downstreams: Map[OutPort, InPort],
+      override val upstreams: Map[InPort, OutPort],
+      override val materializedValueComputation: MaterializedValueNode,
+      override val attributes: Attributes) extends Module {
 
     override def replaceShape(s: Shape): Module = {
       shape.requireSamePortsAs(s)
@@ -404,14 +387,18 @@ object StreamLayout {
         |""".stripMargin
   }
 
+  object CompositeModule {
+    def apply(m: Module, s: Shape): CompositeModule = CompositeModule(Set(m), s, Map.empty, Map.empty, Atomic(m), Attributes.none)
+  }
+
   final case class FusedModule(
-    override val subModules: Set[Module],
-    override val shape: Shape,
-    override val downstreams: Map[OutPort, InPort],
-    override val upstreams: Map[InPort, OutPort],
-    override val materializedValueComputation: MaterializedValueNode,
-    override val attributes: Attributes,
-    info: Fusing.StructuralInfo) extends Module {
+      override val subModules: Set[Module],
+      override val shape: Shape,
+      override val downstreams: Map[OutPort, InPort],
+      override val upstreams: Map[InPort, OutPort],
+      override val materializedValueComputation: MaterializedValueNode,
+      override val attributes: Attributes,
+      info: Fusing.StructuralInfo) extends Module {
 
     override def isFused: Boolean = true
 
diff --git a/akka-stream/src/main/scala/akka/stream/impl/fusing/ActorGraphInterpreter.scala b/akka-stream/src/main/scala/akka/stream/impl/fusing/ActorGraphInterpreter.scala
index a41f8c8fd8..1f82637e73 100644
--- a/akka-stream/src/main/scala/akka/stream/impl/fusing/ActorGraphInterpreter.scala
+++ b/akka-stream/src/main/scala/akka/stream/impl/fusing/ActorGraphInterpreter.scala
@@ -8,7 +8,7 @@ import akka.actor._
 import akka.event.Logging
 import akka.stream._
 import akka.stream.impl.ReactiveStreamsCompliance._
-import akka.stream.impl.StreamLayout.{ CopiedModule, Module }
+import akka.stream.impl.StreamLayout.{ CompositeModule, CopiedModule, Module }
 import akka.stream.impl.fusing.GraphInterpreter.{ DownstreamBoundaryStageLogic, UpstreamBoundaryStageLogic, GraphAssembly }
 import akka.stream.impl.{ ActorPublisher, ReactiveStreamsCompliance }
 import akka.stream.stage.{ GraphStageLogic, InHandler, OutHandler }
@@ -29,13 +29,9 @@ private[stream] case class GraphModule(assembly: GraphAssembly, shape: Shape, at
   override def subModules: Set[Module] = Set.empty
   override def withAttributes(newAttr: Attributes): Module = copy(attributes = newAttr)
 
-  override final def carbonCopy: Module = {
-    val newShape = shape.deepCopy()
-    replaceShape(newShape)
-  }
+  override final def carbonCopy: Module = CopiedModule(shape.deepCopy(), Attributes.none, this)
 
-  override final def replaceShape(newShape: Shape): Module =
-    CopiedModule(newShape, attributes, copyOf = this)
+  override final def replaceShape(newShape: Shape): Module = CompositeModule(this, newShape)
 
   override def toString: String = s"GraphModule\n  ${assembly.toString.replace("\n", "\n  ")}\n  shape=$shape, attributes=$attributes"
 }
diff --git a/akka-stream/src/main/scala/akka/stream/impl/fusing/Fusing.scala b/akka-stream/src/main/scala/akka/stream/impl/fusing/Fusing.scala
index 9af78b8837..14f81c057d 100644
--- a/akka-stream/src/main/scala/akka/stream/impl/fusing/Fusing.scala
+++ b/akka-stream/src/main/scala/akka/stream/impl/fusing/Fusing.scala
@@ -246,7 +246,7 @@ private[stream] object Fusing {
                       struct: BuildStructuralInfo,
                       openGroup: ju.Set[Module],
                       indent: Int): List[(Module, MaterializedValueNode)] = {
-    def log(msg: String): Unit = println(indent + msg)
+    def log(msg: String): Unit = println("  " * indent + msg)
     val async = m match {
       case _: GraphStageModule ⇒ m.attributes.contains(AsyncBoundary)
       case _: GraphModule      ⇒ m.attributes.contains(AsyncBoundary)
@@ -275,7 +275,7 @@ private[stream] object Fusing {
            *  - we need to register the contained modules but take care to not include the internal
            *    wirings into the final result, see also `struct.removeInternalWires()`
            */
-          if (Debug) log(s"graph module ${m.toString.replace("\n", "\n" + indent)}")
+          if (Debug) log(s"graph module ${m.toString.replace("\n", "\n" + "  " * indent)}")
 
           // storing the old Shape in arrays for in-place updating as we clone the contained GraphStages
           val oldIns = oldShape.inlets.toArray
@@ -356,7 +356,7 @@ private[stream] object Fusing {
             subMatBuilder ++= res
           }
           val subMat = subMatBuilder.result()
-          if (Debug) log(subMat.map(p ⇒ s"${p._1.getClass.getName}[${p._1.hashCode}] -> ${p._2}").mkString("subMat\n  " + indent, "\n  " + indent, ""))
+          if (Debug) log(subMat.map(p ⇒ s"${p._1.getClass.getName}[${p._1.hashCode}] -> ${p._2}").mkString("subMat\n  " + "  " * indent, "\n  " + "  " * indent, ""))
           // we need to remove all wirings that this module copied from nested modules so that we
           // don’t do wirings twice
           val oldDownstreams = m match {
diff --git a/akka-stream/src/main/scala/akka/stream/impl/fusing/GraphStages.scala b/akka-stream/src/main/scala/akka/stream/impl/fusing/GraphStages.scala
index 4ccc35bf5b..c51f059e2a 100644
--- a/akka-stream/src/main/scala/akka/stream/impl/fusing/GraphStages.scala
+++ b/akka-stream/src/main/scala/akka/stream/impl/fusing/GraphStages.scala
@@ -25,10 +25,9 @@ import scala.util.Try
 private[akka] final case class GraphStageModule(shape: Shape,
                                                 attributes: Attributes,
                                                 stage: GraphStageWithMaterializedValue[Shape, Any]) extends Module {
-  def carbonCopy: Module = replaceShape(shape.deepCopy())
+  def carbonCopy: Module = CopiedModule(shape.deepCopy(), Attributes.none, this)
 
-  def replaceShape(s: Shape): Module =
-    CopiedModule(s, Attributes.none, this)
+  def replaceShape(s: Shape): Module = CompositeModule(this, s)
 
   def subModules: Set[Module] = Set.empty
 
diff --git a/akka-stream/src/main/scala/akka/stream/io/SslTls.scala b/akka-stream/src/main/scala/akka/stream/io/SslTls.scala
index 913bdbae91..cc8c5e4488 100644
--- a/akka-stream/src/main/scala/akka/stream/io/SslTls.scala
+++ b/akka-stream/src/main/scala/akka/stream/io/SslTls.scala
@@ -9,7 +9,7 @@ import java.util.Optional
 
 import akka.{ NotUsed, japi }
 import akka.stream._
-import akka.stream.impl.StreamLayout.Module
+import akka.stream.impl.StreamLayout.{ Module, CompositeModule }
 import akka.util.ByteString
 import javax.net.ssl._
 
@@ -128,7 +128,7 @@ object SslTls {
 
     override def replaceShape(s: Shape) =
       if (s == shape) this
-      else if (shape.hasSamePortsAs(s)) copy(shape = s)
+      else if (shape.hasSamePortsAs(s)) CompositeModule(this, s)
       else throw new IllegalArgumentException("trying to replace shape with different ports")
   }
 
diff --git a/akka-stream/src/main/scala/akka/stream/scaladsl/BidiFlow.scala b/akka-stream/src/main/scala/akka/stream/scaladsl/BidiFlow.scala
index a0f071cc27..1ab202d56a 100644
--- a/akka-stream/src/main/scala/akka/stream/scaladsl/BidiFlow.scala
+++ b/akka-stream/src/main/scala/akka/stream/scaladsl/BidiFlow.scala
@@ -116,12 +116,7 @@ final class BidiFlow[-I1, +O1, -I2, +O2, +Mat](private[stream] override val modu
   /**
    * Turn this BidiFlow around by 180 degrees, logically flipping it upside down in a protocol stack.
    */
-  def reversed: BidiFlow[I2, O2, I1, O1, Mat] = {
-    BidiFlow.fromGraph(GraphDSL.create(this) { implicit b ⇒
-      reversed ⇒
-        BidiShape(reversed.in2, reversed.out2, reversed.in1, reversed.out1)
-    })
-  }
+  def reversed: BidiFlow[I2, O2, I1, O1, Mat] = new BidiFlow(module.replaceShape(BidiShape(shape.in2, shape.out2, shape.in1, shape.out1)))
 
   /**
    * Transform only the materialized value of this BidiFlow, leaving all other properties as they were.
@@ -137,7 +132,7 @@ final class BidiFlow[-I1, +O1, -I2, +O2, +Mat](private[stream] override val modu
    * only to the contained processing stages).
    */
   override def withAttributes(attr: Attributes): BidiFlow[I1, O1, I2, O2, Mat] =
-    new BidiFlow(module.withAttributes(attr).nest())
+    new BidiFlow(module.withAttributes(attr))
 
   /**
    * Add the given attributes to this Source. Further calls to `withAttributes`
diff --git a/akka-stream/src/main/scala/akka/stream/scaladsl/Flow.scala b/akka-stream/src/main/scala/akka/stream/scaladsl/Flow.scala
index 76bed8a5f7..e45d18a7c6 100644
--- a/akka-stream/src/main/scala/akka/stream/scaladsl/Flow.scala
+++ b/akka-stream/src/main/scala/akka/stream/scaladsl/Flow.scala
@@ -28,7 +28,7 @@ import akka.NotUsed
  * A `Flow` is a set of stream processing steps that has one open input and one open output.
  */
 final class Flow[-In, +Out, +Mat](private[stream] override val module: Module)
-  extends FlowOpsMat[Out, Mat] with Graph[FlowShape[In, Out], Mat] {
+    extends FlowOpsMat[Out, Mat] with Graph[FlowShape[In, Out], Mat] {
 
   override val shape: FlowShape[In, Out] = module.shape.asInstanceOf[FlowShape[In, Out]]
 
@@ -314,12 +314,12 @@ object Flow {
     fromSinkAndSourceMat(sink, source)(Keep.none)
 
   /**
-    * Creates a `Flow` from a `Sink` and a `Source` where the Flow's input
-    * will be sent to the Sink and the Flow's output will come from the Source.
-    *
-    * The `combine` function is used to compose the materialized values of the `sink` and `source`
-    * into the materialized value of the resulting [[Flow]].
-    */
+   * Creates a `Flow` from a `Sink` and a `Source` where the Flow's input
+   * will be sent to the Sink and the Flow's output will come from the Source.
+   *
+   * The `combine` function is used to compose the materialized values of the `sink` and `source`
+   * into the materialized value of the resulting [[Flow]].
+   */
   def fromSinkAndSourceMat[I, O, M1, M2, M](sink: Graph[SinkShape[I], M1], source: Graph[SourceShape[O], M2])(combine: (M1, M2) ⇒ M): Flow[I, O, M] =
     fromGraph(GraphDSL.create(sink, source)(combine) { implicit b ⇒ (in, out) ⇒ FlowShape(in.in, out.out) })
 }
@@ -354,7 +354,7 @@ final case class RunnableGraph[+Mat](private[stream] val module: StreamLayout.Mo
   def run()(implicit materializer: Materializer): Mat = materializer.materialize(this)
 
   override def withAttributes(attr: Attributes): RunnableGraph[Mat] =
-    new RunnableGraph(module.withAttributes(attr).nest())
+    new RunnableGraph(module.withAttributes(attr))
 
   override def named(name: String): RunnableGraph[Mat] = withAttributes(Attributes.name(name))
 }
@@ -928,8 +928,6 @@ trait FlowOps[+Out, +Mat] {
   def conflateWithSeed[S](seed: Out ⇒ S)(aggregate: (S, Out) ⇒ S): Repr[S] =
     via(Batch(1L, ConstantFun.zeroLong, seed, aggregate).withAttributes(DefaultAttributes.conflate))
 
-
-
   /**
    * Allows a faster upstream to progress independently of a slower subscriber by conflating elements into a summary
    * until the subscriber is ready to accept them. For example a conflate step might average incoming numbers if the
diff --git a/akka-stream/src/main/scala/akka/stream/scaladsl/Sink.scala b/akka-stream/src/main/scala/akka/stream/scaladsl/Sink.scala
index 396298f44f..691a4e4469 100644
--- a/akka-stream/src/main/scala/akka/stream/scaladsl/Sink.scala
+++ b/akka-stream/src/main/scala/akka/stream/scaladsl/Sink.scala
@@ -58,7 +58,7 @@ final class Sink[-In, +Mat](private[stream] override val module: Module)
    * only to the contained processing stages).
    */
   override def withAttributes(attr: Attributes): Sink[In, Mat] =
-    new Sink(module.withAttributes(attr).nest())
+    new Sink(module.withAttributes(attr))
 
   /**
    * Add the given attributes to this Source. Further calls to `withAttributes`
diff --git a/akka-stream/src/main/scala/akka/stream/scaladsl/Source.scala b/akka-stream/src/main/scala/akka/stream/scaladsl/Source.scala
index 802be68ccc..d65ee7bbde 100644
--- a/akka-stream/src/main/scala/akka/stream/scaladsl/Source.scala
+++ b/akka-stream/src/main/scala/akka/stream/scaladsl/Source.scala
@@ -132,7 +132,7 @@ final class Source[+Out, +Mat](private[stream] override val module: Module)
    * only to the contained processing stages).
    */
   override def withAttributes(attr: Attributes): Repr[Out] =
-    new Source(module.withAttributes(attr).nest())
+    new Source(module.withAttributes(attr))
 
   /**
    * Add the given attributes to this Source. Further calls to `withAttributes`