7D+100-400+ 1.4XII=no focus
The Canon and the Kenko both report just differently.
As mentioned with an aperture above 5.6 everything but the 1D series won't focus. The Kenko DGX series lie to the camera telling it that the max aperture is less than 5.6 even though it reports the true aperture. Thus the lens will still attempt to autofocus.