For fellow owners of a Canon 1Dx: there’s a firmware update that offers new functionality. Autofocus and exposure controls as well as customization settings have been enhanced. Go here to download.
Details of the upgrade here. And the upgrade works: I did it this morning.
For others: always check that your camera’s firmware is up to date. At least a few times a year, check, and if necessary, upgrade. Else you lose out on bug fixes and new functionality.