^^JJmc, I don't quite understand your point here.
Shooting in full manul is, FULL manual. Let's say 1/100, F4 and ISO 200. If you want -1 light stop, change one of those setting. Either drop to 1/200 or F5.6 or ISO 100. Letting the camera decide which setting to move would not be FULL manual. So it makes senses that there is no such thing.
That's what I thought too so I must not be understanding what JJmc is trying to do and what others are saying is the issue.
I'm not by my camera right now to test the AEB setting but I thought for sure when I did play around in manual mode I could change anything I wanted and it did not take three shots when I pressed the shutter.