Roll Back

I was driving my 17 year old Tercel the other day. It runs like stink and has never had any major repairs.
Anyway, I'm stopped at a light. The car is on a slight incline and suddenly starts slowly rolling backwards. Now I know I have my foot on the brake and I check to see that I'm not in Reverse (which I'm not.). The car continues to roll back and I'm hoping I'm not going to hit the guy behind me. I put the car in Park, it's still rolling. I put on my E brake, the car stops. Sigh of relief.

I am told by the "brake guy" at the garage later that day he can't find anything wrong with the brakes...yet.

"The E brake is your friend." he says.

Good advice.
I haven't driven the car since.

Note: "Sketch" is loosely based on one by artist William Kentridge.