When Urkel and Carl are stuck on the table after being shrunk, some of the items change between shots. Also, the Pringles container goes from standing to lying down then standing again, even before Urkel accidentally knocks it over.
In the overhead shot of Urkel waving at Waldo, Urkel's foot goes over the cover of the book, even though the book is supposed to be higher up than him.
When Eddie triggered the transformation chamber, it caused Carl and Steve to enlarge back to normal size and enlarge Mr. Buttons the cat into a giant, but Harriette, Eddie and Laura didn't enlarge when they were around the chamber.