"In the AFMA menu, when When Adjust by Lens is selected, powering off then on resets the setting (or W/T settings for a zoom lens) to zero, and also clears out a manually entered lens serial number. If I set it to All by Same Amount, the setting entered is retained...but, powering off actually changes the setting to Adjust by Lens, which is zeroed out. Even setting it to Disable and power cycling results in it being set to Adjust by Lens."
"The same reversions occur if the camera goes into standby mode - when it's woken up, the AFMA setting, regardless of where it was left, reverts to Adjust by Lens with the previously set value(s) zeroed out."
I have verified the issue with my 1D X. Expect a firmware update to resolve this bug.
Visit Neuro's "My name is John, and I'm an EAV" post in the forums for more information or to join the discussion. (thanks Sean)