http://www.dchome.net/viewthread.php?tid=949406&extra=page%3D1
(in Traditional Chinese, Google English Translation Here)
It is told that the scratches appear on different positions on the sensor of his unit against his friend's, though. But the worst thing is that the scratch is visible when pictures are taken at small apertures that are smaller than f/11, say, f/13. And he actually posts some of those sample photos in his opening post above and they just look so terrible! >:={
Btw, that user feels rather upset and frustrated after he consulted the local Pentax service centre and was informed that it would not be covered by the Warranty, as it is just a scratch after all. But the user does feel that it is totally not justified as the scratch is surely not caused by himself, as he knows well himself! He further told that his friend is luckier as the same problem was discovered since he asked for a check from his friend but whose unit was still under the first 10-day return period so that he could just arrange a replacement with his shop. (But then who will be the next unlucky guy? Just think about where that replaced unit would go!)
In fact, these two cases are not anything isolated regarding the Pentax QC. As although I did not tell that publicly before, my brand new Olive K-m Special Edition did suffer the same as it was found shortly that the sensor of mine did have a considerably small but obvious scratch on it either, just after about twenty day of use and I am almost sure that that scratch was from the factory but by no means was caused by my normal use. Look at the photos below:-
The second image above is the crop of the first picture to show more clearly for how the scratch is actually located on the sensor. Although it is quite visible, yet the "dust" effect is not much visible on the actual pictures and thus I just opted to ignore the issue after all, unlike the reported K-5 cases above. (Still lucky me!)
As for that new K-5 victim above, he actually also owned a K-x and K-7 before but did never see any similar problem, which was the same for me for not having seen anything similar with my previous units of Pentax DSLRs like the *ist Dx and the K100D.
Indeed, I believe the scratch is on the AA (Anti-Aliasing) filter of the sensor, which is very hard actually - which is harder than typical glass with refractive index of 1.5! (just believe it or not!) As such, I won't believe that any normal use (or just without the first touching on the sensor for my case) could cause a scratch, unless the scratch was just born from the factory! But then, whose factory did the Evil come from? The camera maker? The sensor maker? Who knows? But one thing is for sure, the end-users suffer and thing is not arguable and it must be classified as "user errors" after all ( as the users can by no means prove that it is just not their fault! >:-( ).
Update (11-8):-
1. Yet another K-5 user has just reported the same issue with his K-5. The serial number of his unit is very close, both are with head #382731X. He also posted the image taken with his unit and the scratch appears to be very similar. As such, it has been verified to be a production problem now! So, for all potential K-5 buyers, just beware!
2. As in the latest Post #135 by the OP of the above thread, that poor K-5 owner is still fighting (to death, he said) for a brand new replacement of his body. I just wish all the best to him although I am really not optimistic after all, according to my various previous different experiences to deal with the HK local Pentax agent and their principal behind, i.e., Pentax HQs in Japan (Now Hoya). The contact points at Japan usually just opted to ignore my emails or even mails sent directly to them and they just never bothered to handle any direct complaints from foreign users! >:-\
Read Also:-
Ten Reasons for Thinking Twice before Decided on a K-5..
Some Reported K-5 Faults (Defects and/or Bugs)
My K-r First Hands-ons (Tested Twice)
K-r Defect Reports
K-x' Durability/Production Quality is Just a Joke!
The Quality and Warranty Crises (Re: K-x and Pentax)