Originally posted by cali92rs
That's great to know

I was not planning to download the firmware because it seemed only to add support for the new Pentax TC. But if it makes a difference with the Kenko TC (which i have) I will give it a try

Thanks Mike. It confirms Asahi Man previous comments.
So the SDM+TC problem was more of an AF-related camera firmware issue.
The firmware is also probably made to support contrast AF+TC.
It also confirms that, as it is the case with the 1.7X converter, the resultant focal/aperture transmission is indeed made by the TC, not by the camera.
It also means that this transmission is effective for older classic AF cameras (and non SDM ones).