Thank you for that. Interesting. I imported the pdf printed version (which FF displays correctly) back into Xara, and exported it via xara pdf export and the problem came back.
The PDFs can be found at http://www.tonero.me.uk/jf_eventfiles/newsletter7p4.pdf and http://www.tonero.me.uk/jf_eventfile...letter7p4x.pdf
I don't want to waste your time, but if you have any further observations I'd be interested.