This also happens with Dungeon Entrances and City Entrances up on the Overland map

i believe that's intended behavior, since the keys are assigned to the same action on the ? reference

Bug or not, it's comfortable.

It's really an intentional feature to simplify the UI.

While I understand the reasoning for doing it, there is value in allowing players the choice of whether or not to have them do the same thing.

For instance, if I accidentally go to the wrong stairs, it's made very obvious when I try to, say, ascend, only to find that the key isn't working, because there's no "up" stairs, there. With the current setting, I'd only know that I'd gone the wrong way after the action, which could cause problems.