Personally I think it sucks that nobody told you that this may happen! At the end of the day, you were bright enough to jump off once you had reached the point of no return, however not everybody might have had the same sense. Obviously now you know, you wont let this horse ever stop, but its simply bad management not to keep you informed, and I feel you have a valid grieviance against the RS that didnt tell you, and potentially put you in a very dangerous situtation. At the very least you deserve an apology! Things like this drive me mad, not least because breaking a leg (yours) on the middle of the moors is far more serious than in an urban area where an ambulance etc can be with you in a very short space of time. The fact that you were shouted at by the leaders is pretty inexcusable too, as reallly if they new there was even a chance of it happening they should have been a) with you not with you at the front, and b) off their horses sorting the situation out, not relying on you who was obviously quite shocked to save their saddle. Sorry, rant over, I'm sure you are very happy riding with this school, and should congratulate yourself on dealing with it so well. You can always chalk it up to experience - I'm sure you wont let it happen again.
Best of luck for future rides