I'm at work & can't look at it in game, but do you mean it's a false door? It won't open? There are many doors like that in the older BR maps. The designers put them there for decoration.
OR, do you mean it opens but goes nowhere? In that case I guess the designer just goofed.
I thought I didn't make sense to have another door/stairs at the top level. But I see now there's 'room' for another level, so it does make sense (as decoration). Forget it.