See what Peter Fang, our knowledgeable Pentaxian and long-time brand supporter who bought every Pentax "flagship" DSLR, found with his K-5 and what he writes after that:-
http://forums.dpreview.com/forums/read.asp?forum=1036&message=37092371 (Part 1)
As the discussion quickly reached the 150 posts upper limit for less than 24 hours, he has opened another part for further discussions:-
http://forums.dpreview.com/forums/readflat.asp?forum=1036&thread=37101106 (Part 2)
Besides, see also what is quoted from a K-5 user for what he has been made known from the Hong Kong Pentax sole agent:-
http://www.dchome.net/viewthread.php?tid=949406&page=25#pid11318050, quoted:-
"According to Jebsen,
The spot was actually appeared on the back of the CMOS,
Not at the front ......"
So, the "stains" and spots are actually underneath the AA filter, not above it. So, this must be a manufacturing defect, undoubtedly. But on the other hand if the most unfortunate user has the stains above it, i.e., in front of the AA filter, would Pentax still admit the problem and give him/her a replacement? :-o
Update: Lately, near the end of the "Part 2" DPR discussion thread above (at the time of updating this post), we see these evidence photos, which confirms what is told above, i.e., stains underneath AA filter:-
Then, the user will get such an image, when taken with that defective K-5 with smaller apertures:-
Previous Related:-
Nice Summary and Suggestions on the Scratched K-5 "Sensor" Reported Cases
Scratched "Sensor" Cases of the K-5 Units - Quality Issue of the AA Filters Manufactured by Pentax?
Scratched Sensors of Brand New K-5 Units