It is ironic that this question should come up today. I was at my LBC mechanic today, and he was showing me a MGB with the same cloudiness around the four corners of its windshield. He explained that they are from the frost getting in them, and there is no way to remove them.
Perhaps this is the same thing you are seeing?
Paul /ubbthreads/images/graemlins/canpatriot.GIF