Heres one that happened to me some 30 years ago I learnt to play accordion (not very well) to take the load of the only 2 floor singers our folk club had. Some people came from a ceilidh band and played a couple of tunes and sang a couple of songs. I was playing my little set told everyone what i was going to play and the ceilidh band joined in, excellent until i moved into the 3rd tune of my set and they played something completely different, that I didn't know then told me it was a better tune than the one I had learned. Did not play accordion again in public.
Keith