I'm inclined to say that it's an OS or driver issue (I don't recall OS X or Linux users getting this problem, but I have seen Windows users getting this a lot). Have you tried completely uninstalling 4.0.2 and deleting the Dolphin folder in My Documents? Try that, then use the latest development build (not 4.0.2) again.
You could always try reinstalling Windows as well, but that's a bit of a nuclear option.
You could always try reinstalling Windows as well, but that's a bit of a nuclear option.