Last night while driving in rain and windows closed, windshield fogged up - we used defroster on high heat, but did not seem to clear up - even used the (re)circulator button, but still had problem with fog clearing...Yes, we did have some fog outside while driving, but each time an oncoming car passed us we could see that windshield didn't look clear. Had to use tissue to clear window, and after shutting fogger with heat (was getting too hot in car) we saw windshield fog up again and again. Any suggestions or is this a common problem?