The M-Fn button won't toggle through the different AF Selection modes.
Canon 5D Mark III Manual mode One Shot
I have selected all (or other combinations) of AF area selection modes from AF menu 4 (which means I should be able to toggle between them with the M-Fn button after pressing the AF Point Selection Button.
I should be able to: Press the AF Point Selection Button (the one on the upper right that looks like a checkerboard) Press M-Fn one or more times to toggle through AF area selection modes (Spot AF, Expand AF Area, Expand AF Area Surround, Manual Select or Auto Selection of 61 pt AF). What is actually does is just toggle off/on the indicator in the viewfinder that show which AF point is selected (not the selection mode).
I also tried in on AI Servo, with the same response.
And, yes, I did check to make sure that the AF area selection method is set to M-Fn in AF Menu 4 (and not to Main Dial).
I also tried with two different lenses, since some of the focus system functionality is lens dependent.
What have I got set somewhere to restrict this functionality?