Other mistake: When the Dwarfs first leave the mine entrance, the first few animation cells seem to have been omitted, so that at first the entrance is empty and then the Dwarfs appear out of thin air.
Other mistake: Chico sells Groucho a paper with the name of a horse who is sure to win. It says "ZVBXRPL." Chico explains that the name is in code and then sells Groucho a code book. Groucho looks up the name and says "ZVBXRPL, page 34" but he is looking at a right-hand page. Page 34 would be a left-hand page.
Other mistake: In the opening credits the actor Everett Brown is credited as Everette Brown. (00:01:05)