I looked at my K-7 and K-5 now ...
Both my cameras have a number of particles. Some seem to sit on another layer, judging from the umbra/penumbra diameters. So, I guess, a singular dust particle every some and then is unavoidable.
What is different with my K-5 (and the other images I see) is that there is a string of particles (in the upper left quadrant) which other cameras probably don't have.
So, it isn't the stains as such which are the problem, but the string of stains. I marked the stain position (red) in the attached image. As I said, the random stains don't look too different from my K-7.
My K-5 serial is 3830XXX (btw, are there already non 38XXXXX serials out there?).
Last edited by falconeye; 06-23-2012 at 03:11 AM.