This happens to me to with Flash Builder Premium 4.5.1. It is highly annoying and extremely counter-productive. For $700 software this is not acceptable. Adobe, get your act together.
EDIT: Disabling design mode seems to help (on the Window menu, de-select "Enable Design Mode")
Message was edited by: lukevanin
It happens to me too... But i avoid typing while the file is saving so it's not a big issue... it's still annoying cause I must scroll back to my method every time it happens (it happens 1/10 times)
Just ran into this bug. This is Mac only and seems to go away after disabling design view by toggling Window -> Enable Design Mode.