[oregonmon]

I sometimes get this problem. I am wondering if it is the seals that are sticking so hard to it, it prevents it from sliding down. Never gets stuck or goes slow going up. It also seems that moisture plays a part too, when the windows are wet they don't stick. I tried waxing the windows to kind of lubricating them. Not sure if it is really the problem but they seem to go down every time.
Not sure if your situation is as simple.