[Mirroring] An mx Label or mx Text component in a Spark SkinnableContainer won't draw when the layoutDirection is changed to rtl

This was found in build 13830.
I've included a test project that demonstrates this issue.

Steps to reproduce:
1. Create an mx:Label inside of a SkinnableContainer, using a HorizontalLayout, inside of a WindowedApplication that uses a VerticalLayout. (I'm not sure what combination of these components causes the error.) See XMirrorLabelTest.mxml for the layout I used
2. Set layoutDirection to "rtl" in the root WindowedApplication (or perhaps Application, for Flex)

Actual Results:
The Label is no longer drawn. When switched to a Spark Label it is drawn.

Expected Results:
The mx Label is rendered when the layoutDirection is "rtl."