I recently got my 5DII and I noticed the same thing this weekend. I think it is the result of using the anti-clipping feature in the Menu
Highlight Tone Priority? This essentially underexposes by one stop.
Although the 60D is supposed to be an inferior camera, my 60D never demonstrated this pattern.
I also seldom see it, only when I screw up the exposure in the first place or there's a very dark background (like dark green trees) I'd like to raise in pp behind a very bright front subject.