misted windows

I have Pontiac Sunfire 2000, auto, engine 2.2L.
Just very recently it started to happen when I stop on the traffic light or other occasions and staying for a while all my car's windows are getting instantly wet from the back to the front one. I'm like blocked inside not having any vision to drive further. After a while when I drive further all wet are instantly disappearing and all windows are clean again.

The mechanic identified it as a heater core problem and replaced it. But, today when I was driving it happened again. I called him and he doesn't know what to think.

I would appreciate if anybody could advise anything.

Thanks

Is your carpet or floor mats wet?You may have a water leak somewhere.

Thanks for response, movin2stereo.
It has been checked. It's dry. Some people are saying that the windows inside should be cleaned because some residual on the windows can cause this effect.