Sorry you had a bad experience there Dunk but I think you fell foul of a certain sensitivity to Kneeling shots that has developed of late!
Roger Moy has had occasion to mention them in detail in his pre-match briefs & I have detected a small element of heat in the way he talks about them. As I understand it you,
........Must make contact with 3 points, both feet & knee only, so no sitting on a collapsed leg. The cushion/bumbag can be utilised to support the arch at the base of your trailing leg, under the shin.
The supporting wrist cannot be rested on the forward knee & has to be forward of it.
I think that's it in a nutshell. The situation had got so agravated that Roger even mentioned the possibility of banning the Kneeling Shoot if people kept on abusing it. That was either at the Safety brief at GP9 Sywell or the European Championships, I can't remember which now!
Don't feel too bad though mate, if you've been out the game for a while you weren't to know. Don't let it put you off Dowry Hill next year mate.