Hello Jorge,
Printing of extra pages is usually due to margin issues. However, since your reports are showing this behavior with only a few printers, you may be right in saying this issue is not associated with margins.
As far as extra page is concerned, could you please recheck if the printer settings of printers printing an extra page and printers which work as expected is absolutely the same.
In case they are different which are the particular settings that are different?
Regards,
Tuhina