My name is John, and I'm an EAV (1D X AFMA issue)

[neuroanatomist]

More info, also figured out by Trowski.

With AF4 menu option Orientation Linked AF Point set to the default of Same for Both Vert/Horiz, behavior of the AFMA setting is normal. But, when it's set to Select Separate AF Points (which mine was), the AFMA zeroing out occurs.

Simply changing that one setting from default 'breaks' the AFMA behavior, resulting in the phenomenon shown in my video, and resetting that one setting to default restores the correct behavior.

[ahab1372]

Looks like Canon owes Trowski for doing all the research and narrowing down the root cause of the bug