Probably not doing a form feed at the end of each page.
I think I had this problem a long time ago. If I recall correctly we where able to setup the printer to force the form feed between each page. Maybe we told the printer it was "NOT tractor feed" and that was the trick to have the form feed correctly. I'm not 100% sure because I usually don't setup printers myself.
HTH
Diane Robitaille eng.