In one of the scenes when Bart is knocking on Groundskeeper Willie's door, his shoes show inverted colors. The shoes appear white with blue accents instead of the regular blue with white accents. In the next scene, his shoes are back in their correct color.
Bart's mic while he's at the junkyard changes from corded to cordless.
Though Bart's skateboard is inside the shack when it is filled up with corn cream, it appears perfectly clean once picked up.