Kenko/Canon 1.4x question?

That is correct, the 7D will not even try to focus if it knows the effective aperture is smaller than f/5.6. This is because the focus at those apertures are inconstant.

When you use a 1.4X teleconverter with an f/5.6 lens, it has an f/8 effective aperture, and the camera wont even try to focus. If you tape the pins the camera doesn't know the effective aperture of the lens, and it will at least attempt to focus.