FWIW, the Canon Pixma Pro 9500 has this same issue. I have t/t Pixma Pro support 2x about it and they maintain that the pigment inkset will bleed at the edges of paper, especially art paper, if one tries to print borderless. You can always specify a diff media type and twiddle the settings until you get it right, if you must print borderless. What I found really annoying is that even for images printed on canvas without borderless invoked, the driver insist on that 35 mm margin. I amusing up some old canvas 8.5 x 11 stock right now and I have found work-arounds.