Steps to reproduce:
1. Compile and run attached MXML file (or view SWF)
2. Click "Menu 2" in second (bottom) MenuBar
3. Observe area directly below the red menu.
Actual Results:
Slightly transparent rectangle (see screenshot for enlightenment)
Expected Results:
No slightly transparent rectangle
Workaround (if any):
n/a
screenshot-2: Flex 201.3
Doesn't look like a regression.