PopUpManager Modality Issues - "modal background rectangle" is 50 pixels too small!?

I’m trying to get a modal window working, but for some reason, no matter what I do, the only part of the movie that’s modalized is everything but the bottom 50 pixels; apparently the background transparent rectangle thing isn’t being made high enough for whatever reason. Does anyone have any ideas of what’s going on? A demo .fla of the apparent bug is attached. Thanks for the help.