I haven't been in this situation, and in fact I haven't read the exact language myself, but as it was explained to me, you can't be bumped off a mainline jumpseat if the airplane is over weight or out of balance. They'll bump revenue pax or cargo first.

It might seem counterintuitive, but I believe this is to the company's benefit, because it reduces the incidence of stuck or missed commutes. Pilots get where they need to be on a reliable basis. So if they really want to get rid of this system, then #whatevs.