Hmm. Tricky. From the pictures it seems as you have a back focusing problem. But, both of the pictures are up close the the DOF is shallow. You may have moved a bit when pressing the trigger, or there is something wrong with your focusing technique or the camera is defect. Who knows?
The DOF has allready been discussed above. Some other things that come to my mind:
* Unless you use a tripod you don't know if you have moved a bit. I am sometimes swaying when holding the camera and concentrate on focusing. So, you need to do the tests with the camera and subject both fixed.
* The focusing indicator is not trustable. Ignore it as soon as you got the first confirmation. You have to carefully focus on the matte screen and trust your eyes watching the transition of your subject going in and out of focus.
* A Katz (or any other) screen won't help you with this. The only type of screen that is better for manual focusing is a screen made for manual focusing (they are darker with a more coarse etching on them) that are better for showing the small differences when the focus plane moves. I don't know if there is any such screen made for Pentax.
* A magnifier will help you. With a 2-2.5 magnifier attached to the viewfinder you can work more conveniant with the camera on a tripod and get a much improved view of the exact part you are focusing at. Check this thread:
https://www.pentaxforums.com/forums/wanted-items/3956-searching-k10d-2x-magnifier.html
for some options. In my opinion a magnifier is a good thing to have, it will come to use from time to time and it can be cheaper than a new screen.
* A split prism screen is good for manual focusing when it comes to daily use, for normal pictures and snapshot situations. When really critical focusing is necessary a magnifier and a matte screen is better. The split prism is seldom perfectly made.
* Sometimes focus bracketing is the last resort.
I hope the above can help somewhat and that you get this sorted - it's annoying not being sure about the focusing point.