Difference between Pentax K and KA mount?

I just checked the fit of lens-side K mount on a Pentax body with autofocus mount. Seemingly not only the automatic diaphragm, but also open aperture metering works (I'm just looking at the actuators).

The lens-side mount is a Adaptall-2 mount and Tamron state that for an AF camera one needs instead the KA mount (of course not transferring AF information).

What am I overlooking?

Yes, automatic diaphragm and open aperture metering work with regular K-mount lenses. So, does aperture-priority auto mode. KA mount adds support for shutter priority and program modes. KAF adds AF support.

Thank you!

There's a compatibility table at this webpage that explains what works with the different K-mount-type Pentax lenses:
https://www.pentaxforums.com/articles/photo-articles/pentax-k-1-lens-compatibility-guide.html

KA lenses aill work in Program mode on Pentax and Ricoh cameras, I have a Pentax 50mm 1.4 KA on my Ricoh XRP now.