I backed my car up, put the car in park, opened the door and got out. I walked a few feet away when I noticed the car rolling backwards. The open car door caught a fence which stopped the car from rolling any further. My door was bent backwards. I got into the car from the passenger side. The shifter indicated the car was still in park. Earlier in the day, I drove into my driveway, put the car in park and got out. The car continued to roll forward a few feet before I managed to get back in the car and apply the brake. Again the shifter indicated the car was in park.