It not just my curiosity, recently I've received a bugreport concerning one of my AS3 applications. This bug can be reproduced only if the quality in flash player is set to LOW (HIGH/MEDIUM - everything is ok). The bug changes the application behaviour, but it's a mystery for me, why it happens only for LOW quality while quality is said to influence rendering and visual appearance, not the code or behaviour.
Briefly, I have a menu panel (MovieClip) with several items (also MovieClips). Very simple, it appears on a screen after a MouseEvent and a user moves a cursor from one element down to another. When the cursor reaches the edge of the second item, the menu suddenly disappears. In my code panel hiding is set on mouse click or mouse out.
Personally, I think, that the problem is in Tweener, I have to use that old piece of code. The menu panel is shown when mouse is above a user icon, and concurrently with the help of Tweener I produce some simple effects on this icon.
I have explored adobe and firefox (my app is for web browsers and the bug is reported for firefox) bugtrackers, but so far I have found nothing. Maybe misbehaviour of flash player 11 with Arrays, already fixed... I've run out of ideas.
From the docs:
LOW
Specifies low rendering quality: graphics are not anti-aliased, and bitmaps are not smoothed.
If it only happens when rendering it set to low, then it's probably a timing issue - i.e., the bug has always been there, but because you're wrapping up rendering earlier, you can trigger then bug. Is the bug reporter's computer a slow one? Is there a lot happening at once? Is the menu being removed, set to invisible, or repositioned?
Like @jeremynealbrown said, try and separate out your class to a simple project to make sure there's nothing wrong with your logic there.
Another method, override the removeChild() method, and visible and x and y properties to see which one is setting it, then put traces before all calls that call these to see what's triggering it.
If you think the problem is in Tweener, add a MOUSE_OVER listener to the menu panel that calls something like removeAllTweens(), no matter the state of the menu panel. If the bug doesn't happen anymore, this will show you that it's related to the tween engine.