QTR-Quadtone RIP

Hi,

I was printing on Moab Bright White using curves for Epson Velvet, standard inks, three curves  I not concerned about precise results at this time.  Anyway I found that horizontal banding, bands about 1/8-1/4" appeared across the entire image.  I tried changing to unidirectional, various dithers but there was no change.  So then I switched to the Epson Advanced B&W driver and had no problems -- a perfect image.  What's going on?

Jason