CUPS + printer configuration override from clients

[Eugen Wintersberger <eugen.wintersberger@jku.at>]

Hi there, 
I Debian (testing) on our server together with Windows and Ubuntu
Clients.
Since some time my users cannot change from non-duplex to duplex
printing. If duplex printing is switched on for a certain printer 
on the CUPS server the printer will always print double sided no matter 
if I deactivate duplex printing on the clients printer dialog or not. 
I have to problem on the Windows as well as on the Linux clients. 
It was always possible to override the duplex printing configuration on
the server by the clients printing dialog. 

Has anyone an idea what could cause this problem?

thanks 
  Eugen