Character mistake: When Melanie and Scarlett are talking with an (off-screen) wounded Confederate soldier, the soldier says he hasn't heard from his brother since Bull Run. Only Northerners refer to that battle as Bull Run; Southerners have always referred to it as Manassas.
Visible crew/equipment: At Lees Ferry when the stagecoach is crossing the river, there is a shot from on top of the stagecoach. As the camera pans over to the river, a clear shadow of the camera and its film magazine are visible.
Revealing mistake: In the scene where Cathy goes to Wuthering Heights to beg Heathcliff not to marry Isabella, she goes out the door and in the shot you can see they have not put up the photograph that represents outdoors. Instead there is just a wall and two cables hanging down.
Factual error: In the last British battle at Omdurman near the end of the film, the British bugler is shown wearing a Pattern 1903 bandolier - not made until at least 5 years after the film is set.
Other mistake: Just after newlyweds Gil and Lana arrive at Gil's small log cabin, they are visited by a Native American named Blue Back, who brings them a side of venison. Even though it has been pouring rain outside for hours, Blue Back is perfectly dry when he enters the cabin.
Character mistake: On the proclamation announcing a plebiscite on a proposed "monarchy", the adjective "monarchical" is misspelled "monarchial".