Hi, we've had a connecting cabin once and the door was always locked. I suppose if the two parties don't know each other and both request that it be locked there wouldn't be a problem. Same if both wanted it unlocked.
Not sure the third option would arise where one wanted it open and the other locked.
Remember the stafff are there to makle your holiday as pleasurable as possible so some compromise should be achieved without too much fuss.
Now, go find the cocktail bar and have fun!