Interesting... they were scanned by a lab, and they are all definitely white, so I will assume it is something with the lab scanner. Definitely no fur growing on my camera. It's super clean, thus my surprise at the marks.
As for the darkness, I didn't use a polarizer or any type of filter. They were all shot with the 80mm 2.8 Mamiya lens. I don't think it's an even/odd frame thing either. One entire roll has very dark halves of photos. I might need to try the flash test, I suppose.