[printing] duplex doesn't work

[Thorsten]

Using a hp-laserjet under Ubuntu, duplex printing works just fine -
except using emacs. I installed the printing package, but activating the
duplex option does nothing. 
So I copy text from an emacs-buffer to gedit to get a nicely formatted
duplex print, what is kind of embarrassing, even if nobody looks.
How can I make the duplex option work in printing.el?
Cheers
-- 
Thorsten