Short version: ComboBox's dropdown works and renders properly before fullscreen, but not during or after.
I'm not totally sure how to ask this, so I've actually made a page demonstrating the error, with a very simple Flex app, and all three directions you need to experience the problem yourself.
For those of you not daring enough to follow my link above, I'll do my best to explain here. I've built a rather extensive Flex application (not the one in the link) that has some graphs and charts and checkboxes and other controls for those charts. At the bottom of app in a few of the application States, there is a ComboBox (like a <select> tag in HTML). Because this is at the very bottom, when you click it to access it's dropdown menu, Flex thoughtfully has it come out of the top.
This works well until Fullscreen mode. Upon entering fullscreen, I scale everything up with a stage.scaleMode = StageScaleMode.SHOW_ALL. Now when you click on the ComboBox, the dropdown is astonishingly large, and actually drops beneath the ComboBox, causing it to mostly disappear off-screen. The best part is, once you exit fullscreen mode, the dropdown insists on continuing to drop below the ComboBox, which is positioned at the bottom of the app, and so continues to be cut off. Has anyone else run into this beast, stared into it's great maw, and come away victorious?
You can get the code from the View Source in the link, and thank you so much for your time.