When I purchased my K20D, all my lenses back focused and was happy that I could correct them with the Custom Functions. However, my MF lenses, using the focus indication, still back focused and my newly acquired (2 samples) 15mm Limited's back focus was beyond the custom function's ability.
The problem was solved, for me, when I learned of this site:
Andy McMullan Blog Archive Debug mode on the Pentax K20D DSLR
I set a nominal back focus adjustment determined from my lenses. I then went about retesting my lenses and setting the new adjustments - including the 15mm. All was great until I checked the focus indication for my MF lenses. They still back focused but now, only a tiny amount.
I finally corrected the problem by using the debug mode to set the focus indication for the MF lenses and then corrected all my MF lenses through the custom menu.
I am extremely pleased with the results.
As simple as the solution was, I suggest that Pentax, through the AF custom menu, apply the "All" to all the lenses (correct the focus indication) and then be able to modify that correction for individual lenses.