In release 296 of Zork Zero, the Deserted Castle location, just south of the north dirigible hangar, is an outdoor location (has OUTSIDEBIT set). In later versions, it’s indoors. The differences are very few: it changes the graphic used at that location, whether the ground is called “ground” or “floor”, and the response to digging there with the shovel. Still, I argue that this change was a mistake. The location was clearly written as outdoors.
Here’s the room description: “The summer palace of the Kings of Quendor now lies in ruins, unoccupied and uncared for, forgotten for many years. What’s left of the castle can be entered to the east, and a hangar lies to the north.”
Furthermore, the Ruined Hall to the east is clearly identified as “The entrance hall of the summer castle”.
I don’t know why OUTSIDEBIT was removed from Deserted Castle, but I say that’s a bug.