Sometimes when I shoot RAW, the frames I get have a sharp vertical division exactly in the middle. Carefully inspecting, I concluded that there is a lag / mismatch of successive frames creating this. I use Canon 5d mk 3, 64GB 1000x cards. I have this effect even with Default ML settings. The only modules I enable are mlv RAW video, mlv sound, Auto ETTR Always ON.
Here are 3 succesive frames that illustrate the problem.