QPrinter::setFullPage does not set margins to zero

QPrinter printer;
QPrintDialog dlg (&printer);
if (dlg.exec() == QtDialog::Accepted)
{
  printer.setFullPage(true);
//  printer.setPageMargins(QMargins(0,0,0,0)); // explicitly setting the margins to zero, fixes the bug.

  qDebug () << printer.margins().left << printer.margins().top << printer.margins().right << printer.margins().bottom; // Does not return zero (actual values depend on the default printer)

  QPainter p(&printer);
  p.drawRect(0,0,100, 100); // Rectangle will not coincide with the top left of the page.
}