Comment 4 for bug 693393

It is the same for Natty. Manual Duplex doesn't work depending on the printer model and firmware version you'll get multiple copies or the options are ignored.
AFAIS these options are implemented by filtering the output before it is sent to the printer for some models sending an unchanged file, but a different header to other printer models (these seem to rearrange the printing inside the printer itself, depending on the flags sent).

There are slightly different postscript files send by the windows-drivers than by the Linux drivers. For my eyes these differences do not matter (only space), but maybe they matter for the printer firmware?