I have recently bought an Epson L800 printer. When I print 'borderless' 4x6 prints using photoshop, I always get a border down the right hand side and bottom of the print. Also the picture is not 100% perfectly straight on the page. The pictures are already sized to 6x45 in photoshop so no scaling should be required.
I took the printer back to Epson, but they printed the same picture by going into Windows explorer and right clicking, and selecting 'preview'. They printed from there, setting the printer options to borderless (as I had for photoshop) and the picture printed perfectly with no borders. we tried again with photoshop and the border returned.