car rolled downhill while iin park and emergency brake up

I stopped my car at the top of my steep driveway and pulled up the emergency brake then put the car in park but left car running to listen to a song on radio when I noticed a problem in my yard. I got out of my car and left the car door open and music playing for a couple of minutes while I took care of problem. I only partially got back into my car to cut off the engine switch and as soon as I cut off the engine my car started rolling down my driveway still in park and emergency brake up and with me only halfway in the car being pushed with my left leg on the ground across the street and into my neighbors bedroom. It is a very costly accident and I think it wa a failure of my electronic transmission because all was fine till I cut the engine off and that must have caused a glitch in the trnamission to go into neutral while still showing in park.