Megamud doesn't recognize the message for opening a door. So after it opens a door, it will assume it was not opened.
This can be seen when going into rhudar -- it will go back to the fork then come back.
This can be seen when going into the black house, it will do a black star key collecting loop before entering.
I've seen this with the black star key, but what I noticed was the it failed to notice the "unlocked" message rather than the door opened message. It would unlock the door, never try to open it, and go off in search of a key.