I used to have the same problem when exporting to PDF, but oddly enough, it only came up when viewing in Adobe Reader. If I opened the PDF in Foxit Reader, no problem. Lately, I've had Acrobat Pro installed, so PDFs automatically open up in that, and the problem has not resurfaced.

This is all well and fine for when I'm viewing or printing PDFs on my own, but when a PDF is meant for public consumption, these things have to be looked out for. And it's not cut and dry that this is an Adobe Reader problem and not a Xara problem, because the content (the PDF file) is being generated by a Xara product, and something about the way it places certain objects in a PDF file is not liked by Adobe Reader (I would be quicker to blame Adobe Reader if it were not the product of the company that defines the PDf standard in the first place). In my experience, the problem seemed to be limited to certain types of objects (namely elipses/circles), but as we can see from the above screenshot, this is not always the case.

-- Ben