[meaubry]

Yes, Power Window Motors have a safety component included inside of it that is called a PTC. It essentially, acts like a resettable fuse. When the motor has to work too hard, the PTC trips and you have to wait until it resets before it functions properly again.
It is a safety feature on many motors used in vehicles, to avoid having a fire, in case the motor is stalled for long peruiods of time.
In your case, the problem is that it will "act funny", or seem like it isn't functioning at all - once the PTC trips and tries to reset. Which is never a good thing.
As Chris indicated, the solution is to reduce or eliminate the friction causing the current draw to increase. If that can't be accomplished, you may have to use a different motor.

Mike