Not sure if this has been reported already, but: I just hit the button to close the doors a split second too early, before the passenger exchange was completed. Opened them again, closed them again after another split second... except they didn't close. Tried to "open" them again again and close them again, didn't work. Tried to closed them via Tab key... nope, claims they were closed. Tried to reproduce in a new game, opening and closing doors in rapid succession - works flawless. Perhaps the interrupted boarding is the cause?