Guest, above: I was also at a festival "session" led by a couple who sat there with books and music stands, just working their way through their repertoire. A few of us turned up with instruments and songs at the ready, and were completely ignored. Eventually the leaders were served a meal (it appeared to be part of a deal struck with the pub) so the rest of us seized the opportunity and did our own tunes and songs, but as soon as they'd finished eating, the couple continued their little performance, still as if we weren't there. Even a brief "Have you come far?" or something would have been nice - it was a small festival and there were only a few of us.
To me, that was just bad manners.

Marje