Other mistake: On the first morning at Manderlay, as the girl is leaving the dining room, she slips and nearly falls but Frith is there to catch her, but Frith was way into the dining room; there is no way he could have been close enough to catch her.
Other mistake: In the windmill scene, the windmill reverses directions twice to signal the airplane. However when Joel McRae enters the windmill and we see the machinery it is obvious that there is no mechanism to reverse the windmill against the wind.