1. I have had it happen three times - every single one my fault. Now I not only make sure that the caravan can slightly lift the back of the car before moving, but also I deliberately jerk the car forwards as soon as I am on a tarmac surface so that if it is going to jump off, it will do it there and then before I get up any significant speed.

2. The modern Al-ko stabilisers demand extra clearance round the ball. If your new van is the first time you have had an Al-ko you may need to change the ball.

3. Indeed if your ball is old it is theoretically possible that it may have worn.