Transmission Slip Out Of Gear problems of the 2008 BMW 528

For the past 8 months, my car, a 2008 BMW 528i slips out of drive (d) into park (p) as I was backing up & moving forward either from a parking position or as I begin to accelerate from a stop. The gear shift would go from (d) into (p) and cause the car to jerk to a rapid stop. It makes a horrible noise as it grinds to a stop. It requires me to put it back into park and turn it off sometimes and then start it again. I thought I might be doing something wrong until I read all these other posts so I haven't reported it til now. This creates a dangerous situation and I always start slow now fearful that it will jump into p at a higher rate of speed. I could be in a parking lot or anywhere, moving backward or forward when this happens.