I don't see why singers have a problem. If you go to a mixed session then as with other musicians if you start something expect to be joined in with, if you want to sing unaccompainied go to a song circle and instrumentalists if you don't want singing go to an instruments only session - problem solved. The trick with a mixed session is for everyone to be as tollerant as possible.

I have told a singer to shut up I have also told an instrumentalist to shut up whist a singer was doing her bit so tehre you go evenhandedness rules the day.

PS Session at the Hase is tomorrow night(tuesday 9th Oct) see you there! John