Hi Criollo!
As I commented in another post, I got the latest firmware version of Canon (1.0.5).
Also I disconnected everything except exp.override, but the problem stills there.
It seems that the problem is refered with the LiveView, cause when I used exp.override in Manual Mode or in other photo modes( except video) with the LiveView on, and I set the aperture of the lenses in a low value (f22 for example) it doesn't do anything, the picture is too bright ( yes I checked the shutter speed and ISO too), but when I took a photo, the photo is taken correctly.
However in video this doesn't happen, I got what I see from LiveView, so no matter how I tried to change the aperture that it doesn't do anything.
The flickering issue that we are mentioning, is that sometimes the camera realises that the aperture that you set (f22 again) is not the one which is showing in the LiveView so it change is to the correct value, but then turn back again to high f number (f3.5 for example), of course while doing this, you can hear a loud noise of the lenses "crying" what is no good.
This flickering doesn't happen everytime that you set a low f value, it only happens ocassionally especially when you move the camera to a highlight.
I hope that I got explained