Most of the problems occur because the jump seat system closes way too early and the fact that staff are instructed not to contact the Captains directly to request or cancel jumpseats. ( fair enough rule) Non aircrew would not have a clue how to cancel jumpseats by calling crew control if they happen to get on a earlier flight. As for cabin crew......in my experience many of them come to the flight deck very appreciative often with little gifts for the crew which is a nice touch. I see it a more a system fault rather than people not doing the right thing.