UK Sub Enters German Contolled Port

[rkr1958]

This is an odd one. In my game against Randy a French BB and UK sub that were blockading Wilhelmshaven find themselves being closed in on by the German BB, DD and air units. The French BB trying to move finds a hidden German u-boat flotilla and stays put. The UK sub trying to escape after that finds a second hidden u-boat flotilla and instead of staying put in the hex from which it moved it "retreats" to the German controlled port of Wilhelshaven. I've seen naval units remain is port after it's controlling city was captured but I've never seen a ship retreat into a port that is owned by the other side.