Issue 1:
To reproduce: run the material gallery demo; select the "Drop Down Button" from the drawer; click on the drop down button labelled "Free"--get red screen and the stack trace below.

stork:~/flutter/examples/material_gallery> flutter start && flutter logs --clear
Installing SkyShell.apk on device.
android: --------- beginning of main
android: --------- beginning of system
android: I/flutter : ------------------------------------------------------------------------
android: I/flutter : Exception caught while building _DropDownMenu
android: I/flutter : 'packages/flutter/src/widgets/basic.dart': Failed assertion: line 749: '() {
android: I/flutter : "Positioned must placed inside a Stack";
android: I/flutter : return ancestor is Stack;
android: I/flutter : }' is not true.
android: I/flutter : Stack trace:
android: I/flutter : #0 _AssertionError._throwNew (dart:core-patch/errors_patch.dart:27)
android: I/flutter : #1 Positioned.debugValidateAncestor (packages/flutter/src/widgets/basic.dart:749)
android: I/flutter : #2 ParentDataElement.mount.<anonymous closure> (packages/flutter/src/widgets/framework.dart:1262)
android: I/flutter : #3 ParentDataElement.mount (packages/flutter/src/widgets/framework.dart:1252)
android: I/flutter : #4 Element._inflateWidget (packages/flutter/src/widgets/framework.dart:785)
android: I/flutter : #5 Element.updateChild (packages/flutter/src/widgets/framework.dart:664)
android: I/flutter : #6 ComponentElement.performRebuild (packages/flutter/src/widgets/framework.dart:1108)
android: I/flutter : #7 BuildableElement.rebuild (packages/flutter/src/widgets/framework.dart:1037)
android: I/flutter : #8 ComponentElement._firstBuild (packages/flutter/src/widgets/framework.dart:1083)
android: I/flutter : #9 StatefulComponentElement._firstBuild (packages/flutter/src/widgets/framework.dart:1177)
android: I/flutter : #10 ComponentElement.mount (packages/flutter/src/widgets/framework.dart:1078)
android: I/flutter : #11 Element._inflateWidget (packages/flutter/src/widgets/framework.dart:785)
android: I/flutter : #12 Element.updateChild (packages/flutter/src/widgets/framework.dart:664)
android: I/flutter : #13 ComponentElement.performRebuild (packages/flutter/src/widgets/framework.dart:1108)
android: I/flutter : #14 BuildableElement.rebuild (packages/flutter/src/widgets/framework.dart:1037)
android: I/flutter : #15 ComponentElement._firstBuild (packages/flutter/src/widgets/framework.dart:1083)
android: I/flutter : #16 ComponentElement.mount (packages/flutter/src/widgets/framework.dart:1078)
android: I/flutter : #17 Element._inflateWidget (packages/flutter/src/widgets/framework.dart:785)
android: I/flutter : #18 Element.updateChild (packages/flutter/src/widgets/framework.dart:664)
android: I/flutter : #19 ComponentElement.performRebuild (packages/flutter/src/widgets/framework.dart:1108)
android: I/flutter : #20 BuildableElement.rebuild (packages/flutter/src/widgets/framework.dart:1037)
android: I/flutter : #21 ComponentElement._firstBuild (packages/flutter/src/widgets/framework.dart:1083)
android: I/flutter : #22 ComponentElement.mount (packages/flutter/src/widgets/framework.dart:1078)
android: I/flutter : #23 Element._inflateWidget (packages/flutter/src/widgets/framework.dart:785)
android: I/flutter : #24 Element.updateChild (packages/flutter/src/widgets/framework.dart:664)
android: I/flutter : #25 OneChildRenderObjectElement.mount (packages/flutter/src/widgets/framework.dart:1608)
android: I/flutter : #26 Element._inflateWidget (packages/flutter/src/widgets/framework.dart:785)
android: I/flutter : #27 Element.updateChild (packages/flutter/src/widgets/framework.dart:664)
android: I/flutter : #28 ComponentElement.performRebuild (packages/flutter/src/widgets/framework.dart:1108)
android: I/flutter : #29 BuildableElement.rebuild (packages/flutter/src/widgets/framework.dart:1037)
android: I/flutter : #30 ComponentElement._firstBuild (packages/flutter/src/widgets/framework.dart:1083)
android: I/flutter : #31 ComponentElement.mount (packages/flutter/src/widgets/framework.dart:1078)
android: I/flutter : #32 Element._inflateWidget (packages/flutter/src/widgets/framework.dart:785)
android: I/flutter : #33 Element.updateChild (packages/flutter/src/widgets/framework.dart:664)
android: I/flutter : #34 ComponentElement.performRebuild (packages/flutter/src/widgets/framework.dart:1108)
android: I/flutter : #35 BuildableElement.rebuild (packages/flutter/src/widgets/framework.dart:1037)
android: I/flutter : #36 ComponentElement._firstBuild (packages/flutter/src/widgets/framework.dart:1083)
android: I/flutter : #37 StatefulComponentElement._firstBuild (packages/flutter/src/widgets/framework.dart:1177)
android: I/flutter : #38 ComponentElement.mount (packages/flutter/src/widgets/framework.dart:1078)
android: I/flutter : #39 Element._inflateWidget (packages/flutter/src/widgets/framework.dart:785)
android: I/flutter : #40 Element.updateChild (packages/flutter/src/widgets/framework.dart:664)
android: I/flutter : #41 OneChildRenderObjectElement.mount (packages/flutter/src/widgets/framework.dart:1608)
android: I/flutter : #42 Element._inflateWidget (packages/flutter/src/widgets/framework.dart:785)
android: I/flutter : #43 Element.updateChild (packages/flutter/src/widgets/framework.dart:664)
android: I/flutter : #44 ComponentElement.performRebuild (packages/flutter/src/widgets/framework.dart:1108)
android: I/flutter : #45 BuildableElement.rebuild (packages/flutter/src/widgets/framework.dart:1037)
android: I/flutter : #46 ComponentElement._firstBuild (packages/flutter/src/widgets/framework.dart:1083)
android: I/flutter : #47 StatefulComponentElement._firstBuild (packages/flutter/src/widgets/framework.dart:1177)
android: I/flutter : #48 ComponentElement.mount (packages/flutter/src/widgets/framework.dart:1078)
android: I/flutter : #49 Element._inflateWidget (packages/flutter/src/widgets/framework.dart:785)
android: I/flutter : #50 Element.updateChild (packages/flutter/src/widgets/framework.dart:664)
android: I/flutter : #51 ComponentElement.performRebuild (packages/flutter/src/widgets/framework.dart:1108)
android: I/flutter : #52 BuildableElement.rebuild (packages/flutter/src/widgets/framework.dart:1037)
android: I/flutter : #53 ComponentElement._firstBuild (packages/flutter/src/widgets/framework.dart:1083)
android: I/flutter : #54 ComponentElement.mount (packages/flutter/src/widgets/framework.dart:1078)
android: I/flutter : #55 Element._inflateWidget (packages/flutter/src/widgets/framework.dart:785)
android: I/flutter : #56 Element.updateChild (packages/flutter/src/widgets/framework.dart:664)
android: I/flutter : #57 RenderObjectElement.updateChildren (packages/flutter/src/widgets/framework.dart:1487)
android: I/flutter : #58 MultiChildRenderObjectElement.update (packages/flutter/src/widgets/framework.dart:1698)
android: I/flutter : #59 Element.updateChild (packages/flutter/src/widgets/framework.dart:657)
android: I/flutter : #60 ComponentElement.performRebuild (packages/flutter/src/widgets/framework.dart:1108)
android: I/flutter : #61 BuildableElement.rebuild (packages/flutter/src/widgets/framework.dart:1037)
android: I/flutter : #62 StatefulComponentElement.update (packages/flutter/src/widgets/framework.dart:1195)
android: I/flutter : #63 Element.updateChild (packages/flutter/src/widgets/framework.dart:657)
android: I/flutter : #64 ComponentElement.performRebuild (packages/flutter/src/widgets/framework.dart:1108)
android: I/flutter : #65 BuildableElement.rebuild (packages/flutter/src/widgets/framework.dart:1037)
android: I/flutter : #66 WidgetFlutterBinding.buildDirtyElements.<anonymous closure> (packages/flutter/src/widgets/binding.dart:58)
android: I/flutter : #67 BuildableElement.lockState (packages/flutter/src/widgets/framework.dart:970)
android: I/flutter : #68 WidgetFlutterBinding.buildDirtyElements (packages/flutter/src/widgets/binding.dart:53)
android: I/flutter : #69 WidgetFlutterBinding.beginFrame (packages/flutter/src/widgets/binding.dart:28)
android: I/flutter : #70 FlutterBinding._handlePersistentFrameCallback (packages/flutter/src/rendering/binding.dart:186)
android: I/flutter : #71 Scheduler.invokeCallback (packages/flutter/src/scheduler/scheduler.dart:221)
android: I/flutter : #72 Scheduler.beginFrame (packages/flutter/src/scheduler/scheduler.dart:203)
android: I/flutter : #73 _beginFrame (file:///src/flutter/engine/src/out/android_Release/gen/sky/bindings/Customhooks.dart:45)
android: I/flutter : ------------------------------------------------------------------------
android: I/flutter : ------------------------------------------------------------------------
android: I/flutter : Exception caught while building _DropDownMenu
android: I/flutter : 'packages/flutter/src/widgets/basic.dart': Failed assertion: line 749: '() {
android: I/flutter : "Positioned must placed inside a Stack";
android: I/flutter : return ancestor is Stack;
android: I/flutter : }' is not true.
android: I/flutter : Stack trace:
android: I/flutter : #0 _AssertionError._throwNew (dart:core-patch/errors_patch.dart:27)
android: I/flutter : #1 Positioned.debugValidateAncestor (packages/flutter/src/widgets/basic.dart:749)
android: I/flutter : #2 ParentDataElement.mount.<anonymous closure> (packages/flutter/src/widgets/framework.dart:1262)
android: I/flutter : #3 ParentDataElement.mount (packages/flutter/src/widgets/framework.dart:1252)
android: I/flutter : #4 Element._inflateWidget (packages/flutter/src/widgets/framework.dart:785)
android: I/flutter : #5 Element.updateChild (packages/flutter/src/widgets/framework.dart:664)
android: I/flutter : #6 ComponentElement.performRebuild (packages/flutter/src/widgets/framework.dart:1108)
android: I/flutter : #7 BuildableElement.rebuild (packages/flutter/src/widgets/framework.dart:1037)
android: I/flutter : #8 StatefulComponentElement.update (packages/flutter/src/widgets/framework.dart:1195)
android: I/flutter : #9 Element.updateChild (packages/flutter/src/widgets/framework.dart:657)
android: I/flutter : #10 ComponentElement.performRebuild (packages/flutter/src/widgets/framework.dart:1108)
android: I/flutter : #11 BuildableElement.rebuild (packages/flutter/src/widgets/framework.dart:1037)
android: I/flutter : #12 ProxyElement.update (packages/flutter/src/widgets/framework.dart:1242)
android: I/flutter : #13 Element.updateChild (packages/flutter/src/widgets/framework.dart:657)
android: I/flutter : #14 ComponentElement.performRebuild (packages/flutter/src/widgets/framework.dart:1108)
android: I/flutter : #15 BuildableElement.rebuild (packages/flutter/src/widgets/framework.dart:1037)
android: I/flutter : #16 StatelessComponentElement.update (packages/flutter/src/widgets/framework.dart:1141)
android: I/flutter : #17 Element.updateChild (packages/flutter/src/widgets/framework.dart:657)
android: I/flutter : #18 OneChildRenderObjectElement.update (packages/flutter/src/widgets/framework.dart:1614)
android: I/flutter : #19 Element.updateChild (packages/flutter/src/widgets/framework.dart:657)
android: I/flutter : #20 ComponentElement.performRebuild (packages/flutter/src/widgets/framework.dart:1108)
android: I/flutter : #21 BuildableElement.rebuild (packages/flutter/src/widgets/framework.dart:1037)
android: I/flutter : #22 ProxyElement.update (packages/flutter/src/widgets/framework.dart:1242)
android: I/flutter : #23 Element.updateChild (packages/flutter/src/widgets/framework.dart:657)
android: I/flutter : #24 ComponentElement.performRebuild (packages/flutter/src/widgets/framework.dart:1108)
android: I/flutter : #25 BuildableElement.rebuild (packages/flutter/src/widgets/framework.dart:1037)
android: I/flutter : #26 StatefulComponentElement.update (packages/flutter/src/widgets/framework.dart:1195)
android: I/flutter : #27 Element.updateChild (packages/flutter/src/widgets/framework.dart:657)
android: I/flutter : #28 OneChildRenderObjectElement.update (packages/flutter/src/widgets/framework.dart:1614)
android: I/flutter : #29 Element.updateChild (packages/flutter/src/widgets/framework.dart:657)
android: I/flutter : #30 ComponentElement.performRebuild (packages/flutter/src/widgets/framework.dart:1108)
android: I/flutter : #31 BuildableElement.rebuild (packages/flutter/src/widgets/framework.dart:1037)
android: I/flutter : #32 WidgetFlutterBinding.buildDirtyElements.<anonymous closure> (packages/flutter/src/widgets/binding.dart:58)
android: I/flutter : #33 BuildableElement.lockState (packages/flutter/src/widgets/framework.dart:970)
android: I/flutter : #34 WidgetFlutterBinding.buildDirtyElements (packages/flutter/src/widgets/binding.dart:53)
android: I/flutter : #35 WidgetFlutterBinding.beginFrame (packages/flutter/src/widgets/binding.dart:28)
android: I/flutter : #36 FlutterBinding._handlePersistentFrameCallback (packages/flutter/src/rendering/binding.dart:186)
android: I/flutter : #37 Scheduler.invokeCallback (packages/flutter/src/scheduler/scheduler.dart:221)
android: I/flutter : #38 Scheduler.beginFrame (packages/flutter/src/scheduler/scheduler.dart:203)
android: I/flutter : #39 _beginFrame (file:///src/flutter/engine/src/out/android_Release/gen/sky/bindings/Customhooks.dart:45)
android: I/flutter : ------------------------------------------------------------------------

Issue 2: