Revealing mistake: During the shooting in Candieland, right before Django bursts a man's head, a man next to Django who he uses as a shield has his chest burst. The blood pack is very noticeable.
Factual error: When Big Daddy is on the front porch talking to Bettina there is a security camera above and to his right on the porch overhang.
Continuity mistake: In the final scene where Django asks Cora to say goodbye to Miss Lara, he holds his arm with the gun outstretched, but in the next frontal shot he keeps it lowered.
Answer: Django and Schultz killed some of Big Daddy's farmhands, and he wasn't going to let a freed slave kill some of his workers. Schultz knew Big Daddy would come after them for what they did. Plus Django would never let go of a chance to kill a slave owner who was trying to kill him.