Other mistake: Towards the end of the movie, when Superman drops Gus off at the coal mine, Gus begins talking with the coal miners about him and Superman. He then rips open his shirt (as if he had a Superman costume on underneath). How did Gus know that Clark Kent tore his shirt like that in order to change into Superman, or keeps his suit under his clothes at all? The only people who know this fact are the ones who have seen the transformation from Clark to Superman, i.e. the audience.
Other mistake: When Vader first arrives at the station, he and the Commander are walking past rows of troops. If you look carefully, you will see a Stormtrooper in the back row with his helmet tipped so far forward it's almost off.
Other mistake: In the marching up and down the square skit, the guy behind Eric Idle is trying not to laugh. (00:33:35 - 00:34:05)
Other mistake: Scrooge drops several gold coins into Mole's hat and places the hat on Mole's head. When Mole removes the hat, there are at least 40 coins but Rat exclaims, "Twenty gold sovereigns!" (00:00:22)