Playful decor buff is driving me mad

 @to7m     @BlackjackWidow   Well, I am not sure I would call it the 'missing' shape though, because I tested some more: my sim  made clay shape after clay shape, but no others than the already by Carl recognized ones were created. Several ordinary lumps of clay give moodlets when in the room: Inspired, Focused, Energized and Decorated (as well as the Playful from before). One guess is that they are unfinished/remodeled/begun shapes of the kind that when done are suppose to give/or gave these moodlets. But logging out of the game/putting them in household inventory removed this moodlet from the shapeless lumps; so if OP has done that, then those cannot explain the room moodlet.