Sounds to me like their new system to allow anyone to purchase an upgrade is what caused this, as I doubt ticketing would have allowed someone to purchase a first class trip at that close into the flight...

Looks like someone saw they were going to be miserable, decided to take the offer, and upgrade... taking your seat back from you...

Weird though, as I would think once it was given to you, that would take it out of the upgrade inventory available...

Maybe GA Shenanigans? Hooking a friend up, screwing you in the process, since she figured you didn't get a BP from her, that it was safe to do that to you? She might not have considered that someone could have gotten their BP from the PC...