FrameMaker-specific preflight problem

[Steve Rickaby]

I have a bizarre preflight problem. A (grayscale) book with a great many line art illustrations has four (only) that use the same three clip-art images of cartoon characters. I have reduced all color information in these images to grayscale and preflighted them in Acrobat to ensure that there is no information in the C, M and Y channels.

When the images are inserted into the FrameMaker document and PDF is created from it, the appearance in preflight is that a small rectangular 'window' onto part of the four illustrations contains C, M and Y information. This 'window', a square section more or less in the center of each diagram, has the same appearance in all four illustrations that use the clip art. It does not map to the cartoon images, although it clips one of them, and includes a section of my own added vector art.

Anyone any clues? I'm on ancient FrameMaker 7 on Mac, but I've never seen anything like this before. (The 220-odd other vector art illustrations preflight just fine, with everything in the K channel and nothing in C, M and Y, as it should be.)

What might be a clue: all these problem images include a drop-shadow, and the area containing C, M, Y data is aligned with - although not restricted to - the area occupied by the drop shadow. FrameMaker is set to generate only black, with white as cutout.

-- 
Steve