Damn, I just ran into the most annoying bug ever in SP.
I was at the level in Mexico where
Spoiler you're required to play Texas Hold 'Em, and the German accuses you of cheating.
After taking him out in a duel, his partner came up with the hostage, and I had to take him out without killing her. I would shoot him in the head and she'd stumble off to the side, but for some reason it would keep failing me. Finally what I did was I fired a random shot off in the air, and the mission let me continue. I then took him out in Dead Eye normal and then took out his cronies.
Quite annoying.