This happens if you craft the cow outfit before the silk night gown. The game seems hardcoded to expect you to craft the night gown first.
Viewing post in Pokémon Naughty version comments
Update: Yes, going back to craft the night gown fixes the issue. The game sets it in the third slot of your wardrobe, which is what the game seems to always expect to be there, therefore breaking if anything else is there.
At least your save isn't perma-fucked, but I'm still surprised the dev never thought of this happening.