Edit: as usual, a typo :-/ it’s the EOS-1D X we are talking about here
Canon released a firmware update for the Canon EOS-1D X, version 2.0.8 (download).
Firmware Version 2.0.8 incorporate 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. Firmware Version 2.0.8 is for cameras with firmware Version 2.0.7 or earlier. If your camera's firmware is already Version 2.0.8, it is not necessary to update the firmware. The firmware update takes approximately seven minutes.