Just to be clear, you're finding that after some time, you can type in some files, and they don't get marked as dirty?
Yes. And when it happens in this file I have problems with undo: it undos not last changes but some past of them. From 15 july I was see this many times, but have not time to post here. One guess I have - it is somehow connected to ZenCoding, becouse sometimes ZenCoding wrap command make so strange things it hard to discribe and after that I can't undo this corrupted result. It just stuck in this broken code condition and I must revert file from last save.
Next time you see it, could you check and see if it's just a case of the dirty indicator being clipped in the tab label, and the dirty indicator is perhaps still showing in the window title?
Ok, next time I try to closely watch all what will happens.