Automatic Transmission problems of the 2003 Hyundai XG350

I have a Hyundai Xg350 2003. I had three incidents with it: two summers ago, I put the car in reverse and backed up few feet and stopped to look if it was clear to continue. My foot was on the brake, the car was stopped, then suddenly it lurched back, stopped then lurched back again and again, finally it stopped. I reported it to the service people and they said no way that would happen. Last summer, it did it again, but this time it lurched back only once. Last September, backing out of the garage, I stopped, pressed hard on the brakes to let my wife in. She opened the passenger door half way and the car lurched violently backward, with my foot still pressed hard on the brakes. That caused the door to pin my wife against the chimney, then slid and pinned her against an old refrigerator stored in the garage. Luckily the car stopped but not before it caused injuries to my wife. I researched the internet and found several owners of Hyundai Xg350 reporting the exact same problems.