I apologize for starting a new thread; my mailing list mail is cleared pretty quickly. This is a continuation of a previous thread: http://comox.textdrive.com/pipermail/textmate/2007-March/017974.html
In any case, I have managed to get a screenshot of the issue taking place with normal font settings (i.e. no italicization). Screenshot (sorry for the nasty code :-D): http://img144.imageshack.us/ img144/5830/picture6eu8.png . This is actually three separate screenshots composed. On the left is TM behaving normally with AA off, the center is normal AA on behavior, and on the right is the issue taking place.
Deleting the font cache + restart seemed to fix it, but I haven't experimented enough to verify that that is what is actually fixing it.
Thanks, Andy K.