Castle Living Space Anomaly

The Castle Living Space Anomaly, often shortened to CLSA, is an uncommon occurrence within Super Mario 64 that can drastically change the interior of any castle of the game, even anomalous ones such as The Sunken Castle. These changes usually add furniture to the castle to make it feel more lively, rarely even removing paintings altogether. It is noted that the total star count of any copy with this anomaly is usually much lower than the average copy.

The anomaly tends to "favor" anomalous or alternate castles, though it isn't too rare to find the vanilla castle affected by the changes. Regardless of which castle it is, rooms are often repurposed to fit much more basic needs, such as one of the painting rooms getting turned into a kitchen or the basement becoming a proper basement. Rarely, however, rooms can outright vanish to make more space for other things like a guest room.

Theories
It's possible that the castle was always meant to have furniture, but simply got removed in favor of a freer environment. It's also worth nothing that Nintendo has suggested that the Princess has two castles- one for paintings, and one for furniture. Ergo, this anomaly was probably just leftover code for a second castle that may have went unused, which would potentially explain why the anomaly "favors" anomalous or alternative lobbies.