duplex doesn't work - please help

[Helmut Jarausch]

Hi,

I have cups (svn-050219) installed and it's running just fine except 
duplex printing.

On both, an HP 2300dn and an HP 4050N,
the option sides=two-sided-long-edge seems to get ignored.

I have configured these for duplex printing.

lphelp shows
    2-Sided Printing:  -o Duplex=<choice>

       <choice> can be one of the following:

       None  (Off (1-Sided))
====> DuplexNoTumble  (Flip on Long Edge (Standard), default)
       DuplexTumble  (Flip on Short Edge)

and lateron

    Duplex Unit:  -o HPOption_Duplexer=<choice>

       <choice> can be one of the following:

====> True  (Installed, default)
       False  (Not Installed)


Still, it simply prints single-sided only.
What am I missing and how to debug this?

Many thanks for a hint,

Helmut Jarausch
RWTH-Aachen University
Germany