The problem I had with the gathering I mentioned above is that it seemed to be neither a proper session (all join in) nor a sing/playaround (take it in turns and do your thing separately), but a cross between the two - a sing/playaround where some (but not all)people join in with others. I wasn't sure of the etiquette so I didn't say anything to them, as it seemed to be accepted by all the regulars. I just found it a bit off-putting myself, when playing/singing at my turn. I guess I could have reciprocated but I didn't want to, as it didn't seem right to me.