Can you replace your /usr/lib/cups/filter/cpdftocps file by the attached one (again, make sure it gets world-executable)? Then try to print again. Do the jobs come out double-sided now?
Can you replace your /usr/lib/ cups/filter/ cpdftocps file by the attached one (again, make sure it gets world-executable)? Then try to print again. Do the jobs come out double-sided now?