tricky question here.
I don't know how long this has been going on, but I noticed it only recently. My semi-transparent windows have a “fake” square/window beneath them, which is visible (it also project a shadow, but only when the window is in foreground.
Screenshot: (the textedit window serves just as a white backdrop).
Video showing behaviour:
I initially thought this was just TextMate, but I noticed this on terminal.app too (semi-transparent too).
I am running 10.6.6, have no “strange” hacks or input managers installed AFAIR. I understand that this is probably a very exotic bug, so tools that can help me track down the cause are welcome, and I'll gladly accept such an answer.
Thanks in advance,