Depending on the amount of de-centering, it could be a printer issue. I printed my first box of 17x22 Exhibition Fiber on my 3800 and everything was almost but not quite perfectly centered (an amount you could not detect if you had, say 1.5" white margins), consitently on each print. When I started the second box, I found that the de-centering was a little greater (a mm or two), again consistently across each print. I don't really care, but the variation between two boxes of media tell me it could be a printer issue and not a PS issue, so even a media issue if the sheets are not cut to the same size (I have not checked that).