Brownish Staining on Cyanotypes

I have been making a few cyanotypes recently. I have successfully made cyanotypes before. But now, I seem to be consistently getting brown staining for some reason. The staining is on the entire image - light and dark areas inclusive. I am using paper negatives whereas I was using film negatives before. Some of the paper negatives have been oiled. My setup is as follows: I have a glass base. I lay the sensitized paper on top of the glass. I lay my negative on top of the sensitized sheet. Finally I cover with another piece of glass and develop in my UV exposure unit. I have tried different papers with similar results. The interesting thing is that where the paper negative has not covered the sensitized paper, the paper develops into the rich Prussian blue I would expect for the entire image. Does this process not like my paper negatives? I will try a film negative and report the results. Has anyone had similar results?