QTR-Quadtone RIP

When I print in QTR using gloss inks on my R1800, using the Chapin curves or a similar curve I've created from scratch, I'm getting two very thin horizontal pale lines (that's relative to the print heads, they look vertical in a landscape print).  There is a faint line 24 cm from the leading edge of the paper, and a sharp one 8 cm from the trailing edge.  They are in this location regardless of the size of the paper or size of the print!  They do not show up if I print from Photoshop, or using matte ink and paper in QTR.  The obvious workaround is to print the image with enough surrounding white space so the lines fall there, but it would be preferable to find this bug and kill it.  Has anyone else encountered and solved this?

Thanks,
Bill