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.
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.