I've seen upgrades moved back on BA, usually staff, but I know it happened to one commercial passenger in HKG. Apparently, the handling agent (Jardine) knew they had a need, upgraded a full-fare J class pax to F, and just before the door was closed moved the pax back to Club, but into a middle seat. Pax had already received an amenity kit, glass of fizz, etc. The CSD appeared, and re-upgraded the customer saying "BA never do this to valued customers". Nice save by the CSD, box ticking exercise by the handling agent. Pax still goes on about it, even after BA sent some fizzy bubbly as an apology.