I had that problem 3 times. I wasn't sure if it was the remote in my pocket or something faulty. I spoke to my service guy at BMW he said there has been instances on rainy days, when the driver door is open and rain trickles, it messes up a "sensor" causing the windows to roll down. Another thing that may be an issue is a sensitive latch they said.

My car is going back next Friday for diagnosing. I will let you guys know if they find anything.