Slightly over 20 years ago, the same thing happened to me. I stopped at a pedestrian crossing to allow people across and a young motorcyclist ran into the back of me. There was no question at any time that I was in any way to blame. I got out of the car to check the lad was OK, swapped details and informed my insurance company. That was that. Something seems to have gone wrong here. I was under the impression that if you ran into the back of someone it was always, always your fault.