Odd story. Who had upgraded that person? My understanding is that nowadays the computer does upgrades as per some secret recipe, and that gate agents have little latitude. How come a gate agent could cancel his/her upgrade? Or was your gate agent actually a concierge, who might have more latitude?

I once saw the gate agent come on board and un-upgrade someone. Although the guy who got the J seat was not in uniform, he clearly was a captain on his way to FRA. Agent was obviously apologetic. BTW must have been the last pax to get an upgrade, not one confirmed in advance.