Illustrator colour not printing faithfully in quark???

So, here's the thing… hoping someone can help. I have a quark file, with a illustrator logo in place. The logo is a 7519 brown line drawing on a 7506 cream, shaped, background. Both are SPOT colours. All looks fine in quark, and indeed on any PDF produced, but when I print it there is a shadow behind the line drawing cutting thru the cream background. Printer is a Xerox EX700. Have checked the illustrator file and there are no extraneous boxes to interfere or mismatches in colour that would correspond with the shadow. Illustrator file colour mode is CMYK Any ideas as to why this might be happening and how it can be resolved? Cheers Dave