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.
Revealing mistake: When Ellis Brittle lays dead on the cotton field, a blood pack visibly protrudes from his chest.
Revealing mistake: When Django kills big John Brittle, right when he smashes his face on the floor, a cushion pops-up. Most probably hidden among the leaves to soften the fall.
Revealing mistake: Before confronting Stephen, Django shoots Candie's sister. He is up high on the stairs with her on the first floor. He is far to her right. But when he shoots her, she flies straight backwards into the other room, and you can see where her dress was pulled by a rip line.
Revealing mistake: Near the end after Django shoots "Moonlight" and two other guys, Moonlight is on the floor in pain. When he squirms around he puts his right arm out, revealing a wire from under his shirt going up his right arm. Most likely this was used to ignite the squib charge on his right shoulder. (The first shot Django made in this scene was shooting Moonlight in his right shoulder). (02:36:50)
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.