There are firmware updates for the Canon 1D Mark IV (1.1.3) and Canon 1DS Mark III (1.2.2).
1D Mark IV
Enables the center AF point to autofocus when the camera is used with the EF 200-400mm F4L USM Extender 1.4X lens and an Extender, whose combined maximum aperture is f/8.
Fixes a phenomenon in which abnormal images may result when continuous shooting mode is enabled and the image size is set to “RAW” or “RAW+JPEG.
Enables the center AF point to autofocus when the camera is used with the EF 200-400mm F4L USM Extender 1.4X lens and an Extender, whose combined maximum aperture is f/8.