Digital 952AF Flashgun

I have a Digital 952AF/PEN flashgun which worked well enough on my previous Pentax bodies K100, K200, K10, and it still works on a K20. My question is why won't it work on a K-5lls, K-3ll or a K-1. (I can't remember if it worked on the K-5)

Has the march of progress overtaken the flash or am I missing something in setting up the cameras?

So far I've tried, auto, x, Av, and manual modes on the bodies with TTL and manual on the flash. What happens, particularly with TTL on the flash, when I press the back button to focus the gun goes off quite a few times at random. But then will not fire when the shutter button is operated.

Any ideas please?