The bug occured when I was using ML version (1.1.0-ml-2011Dec22) on my Canon 60D
The bug is repeatable and happens when im using bracketing mode.
If I try and take a bracket but I press and hold down the shutter button the first 2 brackets are taken at the same exposure but the 3rd one is fine. If I quickly press and release the shutter button all 3 exposures are taken at the correct different exposure values. I was using the ML bracketing not the one in the non ML default menu.
If you need some more info on settings/setup etc let me know and I will post them.