LaserJet Printing

When duplex printing, the "front" side of every printed page (the odd numbered pages) prints fine, but the "back" side (all even numbered pages) prints with the top/bottom margin shifted downward.   The shift varies from a half inch to several inches, but always seems to end up with about a 1/4 inch bottom margin.  This happens whether printing from Adobe Acrobat, Word, or Pages whenever the "Long Edge Binding" (or equivalent) is selected. When I select "Short Edge Binding," I don't get the shifted margins, but (of course) the back side is upside down.  Interestingly, Pages gives me a second (identically titled) printer option that doesn't have the usual Layout options, but instead treats the document as a photo or something -- and when I print both sides using this interface, it doesn't shift the margins!  So, I can use this option for Pages, but that doesn't help me with MSWord or with PDF documents.

I know I can duplex manually, and that isn't a huge problem when only printing one copy of a short document, but it becomes a problem when the original document contains many pages, or if I'm printing many copies.  My old Brother MFP cost 1/3 the price of this unit, and didn't have this issue.