Hi again fly380
Your mate mentions BA regularly cancelling flights due to crew shortage, which could ( and certainly did ) up until recently mean a shortage of Cabin Crew. The current clamour here is about an apparent shortage of pilots - which is something new.
Rosters (apart from reserve, which we have already "discussed" elsewhere) are generally very stable. However "Forced Draft" can happen to anyone, out of the blue and as far as I am aware at present you have no choice but to accept.
Rgds
PS sorry for any typos, I'm still giggling at Carnage M's repost in another thread.