the car unlocked, the gearshift went into drive, hit a car

I parked the car in the parking lot at the post office. I placed the car in park. I locked the car. It will not lock if the car is not in park. I went into the post office, got in line, and was waiting my turn when a man came into the post office and asked who owned the black Cadillac. I said I did. He said it had just backed out of the parking lot and had hit a car which was entering the parking lot. I ran outside, and my car was stopped against the driver's door of a woman trying to get into the parking lot. I checked on her, then checked my car. The driver's door was unlocked and the gear shift was in drive. Impossible but true. I am having Cadillac check this thoroughly. We have had trouble with the 2016 slamming on the brakes for no reason at slow speeds, and we can feel the accelerator pedal slightly moving under our feet without pressing on it, but this last runaway is such a mystery, I do NOT want another Cadillac SRX. Someone could have been seriously injured. Has anyone else had a runaway locked SRX? One that unlocks itself and places its gear shift in Drive instead of Park?