I was going into an appointment. My mom as with me and wanted to stay in the car. I put it park and left the heat on for her as it's cold out. Within 5 minutes a man came in looking for me saying there was an accident but my mom was ok. I got to the car and it was still running and in REVERSE. It was parked on a flat surface, rolled forward and down a small hill to a flat surface where it hit a car. My bumper needs replacing. The other car has only minor scratches. Worst - my mom was so severely shaken - she's 88 years old and has a mobility issue - walks with a walker.

Subaru said it must not have been fully in park. I say it's either in park or it's not. You have to put your foot on the brake to change gears. My mom leaned over to turn on the radio. Did she knock it out of gear - how is that possible?

How does it go forward on a flat surface if it's in reverse????

I'm too nervous to drive it again without knowing what happened.

Update from Nov 5, 2017: Problem solved. Not a Safety issue.