Wow you're right mine's front focusing too in tungsten light!
I tried out my K20D in the focusing chart here:
Pentax DSLRs: PART-1. Autofocus Adjustment for the Pentax K20D, Custom Setting No 35
(I prefer it to the one you used here)
So when I tried it out, I found all my lenses had to be adjusted about -9. So I did some tests on some objects in the room that had a flat plane and yes the shots were sharper with the -9 dialled in. But when I went to the other rooms here at home the shots were backfocusing!
I was really stumped and now I've read this it confirms it! The other rooms had flourescent lighting and the room I did the initial test is using tungsten lighting.
So I took some photos of photos (haha) on the walls (flat plane) in 1 room with tungsten and 1 with flourescent, shots with the focusing adjusted and shots with no adjustment. I used flash so I didn't need to kill camera shake.
So in the rooms with tungsten the adjustment had sharper shots and in the flourescent room having no adjustment yielded sharper shots.
This sucks. What should I do?
Can anyone else try it out?