I have the same problem, my 50D is in M mode, I've set FPS overide to 23.976 and my exposure to f/4, 1/50th, ISO 200 but when I hit record, the display info seems to indicate that the shutter changes automatically, and I can see from the live view that the exposure has adjusted automatically.
I have Gradual Exposure OFF, Expo Lock OFF, Expo Presets OFF and Expo Override OFF too.
Any hints on what I'm doing wrong?
Also, the FPS Override doesn't seem to work because when I import the files to Resolve, it seems like they were recorded at 30fps.