Baggage handling and checkin staff are two very different teams - the baggage handling after you gave your bag to checkin is usually completely outsourced to the airport bagagge handler. Checkin staff wouldnt load or unload your bag onto aircraft. Is there a reason you believe checkin staff themselves did this?
Also do you have this in writing from BA about being loaded and then unloaded - this is fairly uncommon, unless you miss your plane (or show up at gate at t-19 or so)!