Just what the title says.
This is how I tested it:
Put the camera in M mode. Let's say it's incredible dark, a moonless night with no light pollution. I set the shutter speed to 4s so I don't have to wait a lot of time for each exposure, I just need to frame my shot. f/2.8 (which doesn't matter since the camera can't read that information because the lens is not chipped) and ISO 25600.
Instead of seeing at least some detail in the screen, I just get a dark image and no visible noise moving around.
On the 60D, which has max ISO 12800, I see much more detail (and noise, of course) than on the 6D.
I tried enabling and disabling exposure simulation. I also reseted my config file to defaults just to make sure other options didn't cause the issue, but it still not working.
Now, if I move the exposure wheel, sometimes there's a brief moment where I see exposure override working, but its just for less than a second and doesn't always happen.
I tested this with magiclantern-v2.3.NEXT.2014Mar12.6D113 This was also discussed here: http://www.magiclantern.fm/forum/index.php?topic=9262.0
If you need more information just let me know.