There's a new Comodo upgrade as of a couple of days ago, mostly bug fixes -- 3.0.14.276. Have you tried that to see if it helps?
There's a patch for only two previous versions (one of which is the .268), but that's nearly as big (9 megs) as the full install, so it's pretty much a tossup whether to uninstall/reinstall or overinstall just the patch.
No problems with my XP either, so whatever it is has to be specific to Vista.
(Edit) Yes, only 9 megs as compared with something like 30-plus previously. If I understand correctly, most of that is from a massive overhaul of their "whitelist" database.