I've used Royal Velvets exclusively for buffing Zaino for a few years now and I've never noticed any marring. The only time I notice anything similar to what you're describing is when I try to buff off a coat of Z2/Z5 before it's fully dried, which rarely happens. Are you letting the Zaino dry long enough? If the lines are as shiney as you describe, it really sounds like you're buffing it prematurely or simply not removing all the film. The only thing I could suggest is give it maybe an extra 15 to 30 minutes before you buff. Also, if Z6 makes those lines go away, then it's almost certain to be undried product left on the surface.
