qprintdialog doesn't update printer settings

I am trying to debug a problem of a c++ application based on qt5 (qpdfview) where the printing options are not taken in consideration. Eventually I have discovered that the problem is general and I can reproduce it using the following simple python script:

pyver=5

if pyver == 4 :
 from PyQt4.QtCore import *
 from PyQt4.QtGui import *
else :
 from PyQt5.Qt import *
 from PyQt5.QtGui import *
app = QApplication([])
w=QPrintDialog()
w.show()
if w.exec_() :
 print w.printer().printerName()
 print "source is %d" % w.printer().paperSource()
 print "size is %d" % w.printer().paperSize()
 print "orientation is %d" % w.printer().orientation()
else :
 print "cancelled"

I can immediately verify that the printer options are not changed when I change them in the printer options dialog (started from the Properties button). The same script running against qt4 works as expected.

I am working on a Linux platform