power window motor

I have a 94 BMW 325i convertable with a strange power window problem. The window wouldn't go up on the drivers door but seemed to have power as it tried to respond to the command switch but would only budge a centimeter. I thought "Jam" but inspection of the tracks came up clear. I removed the motor and found that the polarity seemed to be reversed, up was down and vice versa. I replaced the motor and track assembly and it worked fine for a few times. The same problem occurred within a half hour of installation (3 or 4 cycles of the window) It is stuck down, with power, and just pushes a centimeter then stops.