Sigma 120-400 with TC (1 Viewer)

I have the above lens on a Nikon D80 and was thinking of getting a 1.4 TC. I tried one outside the shop and was very pleased with the results except that the AF did not work. I had noted that this lens is not on the list of compatable lenses for the TC on the Sigma website. The shop confirmed this and I thought that this is why the AF did not work.

Can anyone confirm that the AF will not work with this combination or have I missed something. Thanks.