Hate to say it, but if this is happening with manual focus the camera almost cannot be at fault.
The image shows no/little signs of motion blur so the user is almost certainly not focusing properly.
If things look fine to you, then I would have to agree with checking the diopter adjustment in this case.
The Laws of Physics do not change due to the Pentax label on the box. i.e. focusing principles do not change.
Sadly at this point, if you're certain YOU are doing EVERYTHING right, then your equipment is broken. (i.e. the sensor could be way out of alignment)
Do your lab tests. Also try auto focus.
Get us an image with full EXIF data (or dump it for us yourself) so we can examine what the camera has to say.
Until you can determine how the camera behaves under unchanged conditions, you really cannot begin to debug the problem.
I trust you know what you're doing, and I trust you're telling us the truth but we really cannot help much more from the info given.
Last edited by amoringello; 09-21-2010 at 02:57 AM.