Hi, I've been receiving the same basic files from a client for a few years now. The Illustrator (15.10.) file is saved as an Acrobat (10.1.3) PDF then opened in Photoshop (12.1 x64).
In the art is a 50% grey blur like shadow that's some imported raster shape. That blur is over the artboard, with no further tone, color or layers beneath it, so, theoretically, it's on white. Up until this current set of files i'd have no problems importing the pdf in Photoshop, flattening and saving, the blur would transition to white and everything was good. But now, even though when still layered it shows the white to be 0/0/0/0 in cmyk, as soon as I flatten it, that white area is now 0/0/0/3.
I've gone through the Illustrator file and cannot find an new elements, and when I take a previous PDF who's tif file is fine, and open that pdf in Photoshop, I get the same addition of tone. So this tells me something has changed in Photoshop, be it a setting or preference that's been altered.
Can anyone suggest any place to check?
It could be a number of things quite frankly that is creating a scum dot. Color managlement is highly suspect so poke around for about 5 hours and see what you come up with. That's pretty much the process in which you are given considering how well it's implemented across all Adobe products. Get back to us when you find you are at your wits end to share the beauty in all its glory.