Other mistake: In the scene where the Simpsons are viewing the path of the Corvair's Re-entry, the blip representing the spaceship crosses the entire US from North-West to South-East in about three seconds. This is really impossible, even for something going as fast as a spaceship on re-entry would be.
Continuity mistake: In the 'Nightmare on Evergreen Terrace' segment, in Bart's dream you see a shadow of what looks like someone with four knife-fingers. Then when we see who it is, it is Willie holding a rake. But the rake has five tines, not four, so the shadow is wrong.
Continuity mistake: When Bart and Lisa are trying to win back Homer's affection they are sitting on the top of the stairs and push the skateboard with the present on it down the stairs. In the next shot it rolls into Homer's legs yet it would be impossible as he was standing in the main living room which is to the right of the stairs. Pushing the present down the stairs it would go straight into the front door.