I can confirm this problem with a Samsung ML-2580 Series printer.
Duplex printing worked flawlessly in Ubuntu 10.10. With Ubuntu 11.10 it still shows the Duplex-Print options in the print dialog, but the setting has no effect.
The problem occurs in all tested programs (Libre Office Writer, Evince).
I can confirm this problem with a Samsung ML-2580 Series printer.
Duplex printing worked flawlessly in Ubuntu 10.10. With Ubuntu 11.10 it still shows the Duplex-Print options in the print dialog, but the setting has no effect.
The problem occurs in all tested programs (Libre Office Writer, Evince).