There's a scene where Arnold is talking about saving the neighborhood, while Helga is on the roof of a building talking to herself. Arnold is in the street, and there's a man in a white tank top standing in front of him. In another shot, the man is standing behind Arnold, and Helga shoots a plunger at his head. Then in the next shot, the man is back in front of Arnold and his head doesn't have the plunger on it any more.
When Big Bob first asks to keep the pop-up version of the Arnold's neighborhood, he picks up Arnold's house and on the roof it only shows the sky window. Once it gets thrown in the trash the shed suddenly appears next to the sky window.