Caoturing Homeland and holding for 1 turn and winning

I've noticed in certain games that the way to eliminate a person from a game is to take their homeland, the cap and all it's cities, and hold it for 3 turns. In the pst and just now, I saw Player A cap player C and Plaer B takes over all of C's towns. A moves out of C's cap B puts a unit in the empty cap, and the next trun C dies. Shouldnt B have had to wait 3 turns for C to die? Is ths a bug and if so, will it be fixed?