I encountered the same problem with Flexreport but that was due to incorrect paper size. How do measure your print area? did you define the size explicitly?
example: 8.5" x 11" = 612pixel x 792pixel.
in my code:
<Report xmlns="org.print.*" xmlns:mx="http://www.adobe.com/2006/mxml" width="792" height="612" xmlns:reports="templates.reports.*">
Did we have the same approach?
Are you calling printView.validateNow() after calling printView.printGrid.nextPage(). Like the other comment said , sizing greatly helps.