The
problem is solved. There is nothing wrong with the camera. It's
diffraction which causes the blur at small apertures on APS-C sensors.
In my opinion it's too often not mentioned in camera reviews. Or it's
hidden behind euphemisms like "at F 22 diffraction takes it's toll"
instead of: the image is blurred. I'm a bit disappointed.
If you still want to have a look at the sample pictures, the new page is here.