While trying out if this issue has been resolved (it hasn't) https://bitbucket.org/account/notifications/read/44744706/re-issue-1850-advanced-bracketing-with-lv-shows-last-brightest
I somehow got the DSLR taking pictures forever, some of them are being taken with the selected AB algorithm but most of the are being taken without altering the exposure times.
Abortion via scroll wheel turn is not possible when this happens, you have to turn off the camera.
It doesn't happen all the time, but mostly when you press the shutter button without "giving a damn" about the camera has focused on the scene or not (pressing shutter for effect and not waiting for the confirmation beep of the AF)
Also sometimes when this happens, the AF mode changed from AI Servo to ONE SHOT.
I can't really tell how exactly this can be produced except for trying to press the shutter button all the way through not minding about the AF.
Camera is a EOS 550D with tonight's nightly build (February 27th)