My opponent had Callaphe, Beloved of the Sea on board. I played Pacifism targeting it and payed the extra 1. Next turn my opponent played another Callaphe, Beloved of the Sea and chose to have the one with Pacifism on it die. I then tried to play another Pacifism on the new Callaphe, Beloved of the Sea but the game thought the first one was still on the board and made me pay 6 to target it.
Had the same exact bug occur for me as well.