I too, have experienced the turning of backs on me, the singer, and even tuning up and then STARTING A TUNE in the middle of my song. Sometimes I see that person in sessions and take great delight in interrupting her!

Perhaps a tune player may consider that you have started (an unwelcome) song in the middle of their tune? BUT!

If there IS a war going on between singers and instrumentalists, and it would appear that there is, in some quarters, perhaps the fist shots of peace have to be fired?

I speak as a singer who is quite happy to play tunes and listen to others sing or play. Because of this, I refuse to take side, even though it may appear that I am a little hard on singers in this thread (and others).

If I am it is simply for the reason that although some singers well understand why a song from them may not be always welcome, they rather unfairly seem to see this as 'snotty' instrumentalists conspiring together, for the sole reason of preventing them from singing (not that there are not such beings). Are there no 'snotty' singers?

If someone insists on imposing a song where and when it is clear that the majority of participants are perfectly happy and do not need to sing songs, they should not really be suprised if their questionable ill-manners are reciprocated.

As in most conflicts, the two sides (if they are so divided over this issue) have more that unites them that which devides them. The common ground is there and should be looked for. There is, I think basic a lack of understanding of different requirements.

It is fairly simple. One is more about participation, the other is more about performance.

Tune players need fellow players more than they need an audience.

Singers need an audience more than they need fellow players.

Turning one's fellow players into an audience is not much appreciated if or when a show-off instrumentalist does a 'star turn' to their fellow players, when they have come to join in.
It should hardly be suprising if being (repeatedly) turned in to an audience by singers, is not much appreciated.

When these different requirements are recognised, it should be possible to co-exist in peace, shouldn't it?