Whats with the trasfer deadline?

Friend just called me and said His new star Striker was stolen a week after transfer deadline. And they did not have to wait until january to get him. His player vanished at once, but my friend could not buy a replacement as the transfer window had closed.

He played as Peterborough in the first season.

Luckily for him the game crashed during his next match, and he had to load a savegame before he lost Boyd. Can anyone explain how that team could buy his player after the TD had passed. He was not allowed to buy a replacement the very same day because TD had passed