When a tab is selected in a TabBar or TabNavigator, the label in the tab shifts down a single pixel. I spent about 10 hours scouring the web, Flex source, and default CSS trying to find the cause of this shift so I could disable it. I eventually had to simply put a hack in the Button class to reverse the shift after the selection was made. I'm assuming the shift is a feature, not a bug, but it shouldn't be so difficult to disable it. The shift does not occur for ToggleButtonBar, the parent of TabBar.
Should I submit this as a bug? I posted on flexcoders and even in this forum earlier in the month and didn't get any useful responses.