You did not mention if you were changing Flotillas at the same starting base.
I ask this cause it happened to me also when changing flotilla at the same base. Same exact problem.
Don't know any way around it except go out and come back into a save before the request was made and request a transfer to a different base, do a mission and then ask for a transfer to the flotilla I wanted.
It was a pain cause I had to shutdown, restart computer and reload the game.
