Rear window falling down

When I press one of the rear windows to go down on my car (the one behind the driver) it makes the noise as if it's going down then stays in place. If I leave it in the "down" position it will just fall down into the door while I drive along. Then it comes back up when I press the up position. 

I looked at this thread:

http://www.briskoda.net/forums/topic/47196-how-to-remove-octy-ii-door-cards-speaker-sizes/

Do I have to remove the "inner panel" he shows in his pictures once I've removed the door card? Or is the fault with one of the things on the outer panel? What do I do once I've removed this inner panel if so?

Edit: Also this has been "fixed" twice now by a garage. It works for a while then the same problem crops up every 6 months or so. What would I have to do to permanently keep the window from falling down?

Edited 29 January, 201511 yr by mccarf