Go towards the end of the movie where there in Emerald City and the man in green says they cant enter to see the great OZ. He says, "Nobody can see the great OZ, not nobody not no how." his mustache is pointing up in the air. Then when it changes scenes to him again its pointing down. Pretty scary huh!
You know you would wonder if people would catch that this movie has all sorts of changes that aren't really slip ups. This very well might be one, but think of this. Couldn't this be shown this way to show the humor in the movie? Maybe it was one of those RARE moments that director's MEAN to put in the movie.
In an effort to cut the movie's running time down, a number of scenes were deleted. One brief scene that was deleted was the "changing of the guard". The guard halted the conversation, went into his little hut and returned with his mustache reversed. The "Wizard of Oz 50th Anniversary" (1989) edition describes a number of these deleted scenes and the effect they had on the final picture.