I fully agree with Dov - and I might add - "is this only some artifact of display ?" - I wonder if you print or RIP, if this is still the case. There are several settings that one can change in Acrobat that effect how a PDF file might display. We have found that the PDF files that area exported to PDF have fewer issues with display or RIPing, thanks to massive improvements from Adobe and their "export to PDF' tools.