Field data different on screen vs printed

We're having a problem with a Purchase Order print configuration.  Many of our items have different part numbers and descriptions from our vendors.  In order to keep straight what we and they are talking about when we place orders, we are adding a field on our printed PO that has our part number, our description, their part number, their description.

When we add all of these columns to the screen view of the PO layout, they should up just fine and display accurate information.  When we add the same fields to the printed PO, one field, "item" displays the vendor part number instead of our part number (yes, it's correct in the item master).  The vendor p/n shows properly on the printed form where it is supposed to - but also shows up where ours should.  The vendor p/n shows up twice, ours never shows.