OK, this seems to be a weird one. Win 7 & OfficeJet 6500A.
I have created a couple of documents in Word, there's an image in the top right (not the header) & an image in the footer.
When I print single sided, everything prints fine, 2 sided using the duplexer causes the footer to appear further up the page.
If I open the printer properties & go to the advanced tab, there's a check box for minimise margins, if this is un-ticked, the footer appears in the correct place but the image at the top moves down & the other images are scaled differently.
I got over the issue of the page size switching between A4 & letter by un-installing the whole HP crap & reinstalling.
Creating it as a PDF & printing from Adobe reader is the same, which leads me to think this is yet another HP balls up.
Any ideas??