Character mistake: When Dorothy and the others enter the Haunted forest, the sign reads "Witches Castle One Mile." "Witches" is plural. To be grammatically correct, it should have said "Witch's Castle," if one witch, or "Witches' Castle" if more than one.
Character mistake: When the munchkin soldiers first arrive, you can see that some of the munchkins in the front are not beating their chest at the same time. This also happens when the munchkins sing the "fa la la la la" song before the witch arrives. (00:24:25)
Suggested correction: That happens in real life too with real soldiers and live performing actors as much as they try to perfect it because they're human, not machines. Unless there's a rule in the film that a munchkin has to be perfect and can't make mistakes like that, not seeing why this is a movie mistake when this is something that happens in real life.