During the scenes in which the Creeper's bust is sculpted, the degree of completion varies from shot to shot.
In the penultimate scene, De Lange talks about the Creeper in seeming unawareness of his presence, even though the Creeper has already left his place of concealment and is standing right in front of De Lange.
After the Creeper kills De Lange and smashes the bust, Joan runs to the studio door and finds it locked. It would have been much more sensible for her to have tried fleeing the studio while De Lange and the Creeper were fighting.