Rear dome light mystery
 

My rear dome light won't go out for some reason, and it killed the battery before I found out the reason was just that.
I thought I may have touched the switch above the mirror by accident, and when I am in the car and push the switch, it goes out. When I open the door the lights come on, then the front courtesy lights fade out as they should, but the rear one stays on. I tried all the doors to be sure they were closed, and still it comes on and stays on. I finally disconnected the wire so it's out permanently, but it was always fine before.
Any ideas out there????
Thanks