We run a lot of carefully color managed PDFs through Printshop Mail prior to printing. We have noticed an issue where a vector graphic that is a back only gray will sometimes be converted to CMY when it is output to PDF. In the specific case I am currently trying to fix, some 40% black lines on the front of the brochure stayed black only, but all of the 40% black only lines on the back were converted to CMY.

If I look at the elements of the pages in Object Inspector in Acrobat, on the front, a US Web Coated SWOP V2 profile has been applied, but on the back everything says "ColorSpace: ICCBasedCMYK, Profile 41286...(long number).. from Postscript CSA."
It's doubly weird, because we have a joboptions file that we are using to color manage on output that is set to have Printshop Mail leave the color alone. In the input file everything on both sides shows as DeviceCMYK

When I changed this joboptions file to convert everything to a different profile, it still wrote the pages with the profiles above.

When I wrote a PS file instead and converted externally in Distiller, it again wrote with the same odd profiles, so I think we can rule out the Adobe PDF virtual printer settings.

Do you have any other ideas on how we can get Printshop Mail to leave the color of the files alone?