Just got the response from Pentax via their head office in Germany. They confirmed that there is a back focussing problem with the 21mm Limited exclusively. They offered to set up one of my bodies to work in conjunction with the lens, which I refused. I do not wish to take up one body exclusively for that lens. I am waiting on a firmware fix or a chip set change for the lens. I will use it in manual focus only. They are sending me back the two bodies and the two lenses i.e. the 21 and the 16-45 which didn't have a problem and focussed perfectly on the "0" calibration point. I will wait for the 16-50 f2.8 which I should have in ten days to use in lieu of the 21mm Limited. If it is anything like the Canon 17-40L lens which I used on 80 percent of my magazine work, I will probably do the same with it.
Ben