I parked my 2013 ALL4 cooper in our driveway today with E-brake up and the car in gear. After about 5 minutes the car rolled back down with a speed like the engine was on. It did not look like it is slowly accelerating, but more like the engine was engaged! The key was out of the ignition and in the house. I am dumbfounded. I don't know what to think. Can someone shine a light on this? I am worried to leave my teenager in the car now when I am not around. Thanks...