http://tech.groups.yahoo.com/group/ricehigh_pentax/message/937
Reports from K-7 users about sensor stains with photos clearly showing those are posted. And yes, the symptom is exactly the same as the previous K-5's.So, it is almost safe to conclude that it's Pentax' AA filter that causes the problem!
(Source Thread: http://bbs.kakaku.com/bbs/K0000036023/SortID=9944776/#9953651)
After all, the AA filter simply would change in state over time and it is generally guessed that the larger amount of heat from the sensor unit melts the AA filter and thus causing the visible stains. That could explain why the less-hot Pentax models like K-r, K-x and K-m have never had that problem reported. But, at the end of the day, the BIG question is that: Will the next Pentax Flagship have the same persistent problem? Or, will Pentax simply NOT install any AA filter like what they have already done to the Q? That would be the safest "solution" to the issue? Right? ;-)