The safe timer limits need to be adjusted (35fps is too much). Adjust the timers manually and see when the image gets restored.
Cool, so what is basically happening at those shutter speeds?
1/250 is fine for that FPS setting while 1/320 makes it flash.
If i can help in any way...
Also, as i asked above, is the pixel binning method portable from the 5DIII?
One more thing, i noticed that the crop window when shooting raw is a tiny bit narrower than the full frame at maximum resolution.
Not sure if it's a problem with the framing or what.