My Canon 5D has no problem doing Automatic Exposure Bracketing with a Canon lens.
When I use a Zeiss ZF lens with a Cameraquest adapter, my single exposures are OK until I use AEB. As soon as I switch to AEB mode, the exposure reading jumps from 1/8th of a second to 30 seconds, which is way overexposed. The three exposures are then all overexposed.
Have others had this problem? Is there a workaround?