BMW Questions? Ask a BMW Repair Expert for Answers.
I think I might be able to help. When do they go down? Once you turn the car off and get out?
BMW made this year model with what they call "comfort setting". It means that if you hold the unlock button on the key fob all of the windows roll down. If you hold the lock button they should roll back up again. If you weren't pushing the unlock button (or don't have a key fob) then there is something malfunctioning in this system. The first thing I would try is to roll them up and see if it will do it again. If it doesn't, then I would assume the key fob was stuck for and it has freed it's self up. If it does it again, I would take the battery out of the key fob and see if it stops doing it. If it stops, you will need to replace the key fob. If it doesn't stop, there is a short sort in the control module.
They all go down at the same time right? Not one at a time?
If it's one window at a time I would check the micro switch at each window. Here is a bulletin that BMW put out a few years ago about the rear windows doing what you describe but it was because of the switch on each window.
I just wanted to check in and see if you needed any additional information on this question? I haven't yet seen a response or rating since my last suggestion and was hoping to help in any way I can.