I know the proposer can end the proposal at any time, but how does someone who accepts an invitation cancel it (save presumably by exiting the game) if it turns out they can't join after all?
When I first saw this thread, I wondered if the proposal coming up short was due to nothing worse than one or more players changing their mind about joining and not knowing how to uninvite themselves.
If it really is down to people deliberately trying to spoil battle proposals then to hell with them of course, but unless someone is doing this consistently, assuming malice seems a big inference.