Canon has issued a firmware update for the EOS 1D X. Firmware version 2.0.8 provides the following fix:
- Fixes a phenomenon which occurs when the “Shutter button half-press” menu item, configured in “C.Fn5: Operation” > “Custom Controls Menu”, is set to metering start only; depending on when the shutter button is half-pressed, it may initiate AutoFocus.
You can download the firmware update here on Canon’s website.