duplex option ignored with imported Lexmark T430 PPD file

Wed May 11 08:09:32 PDT 2005

I have a Lexmark T430D printer. I got a PPD file for it (from Lexmark site), imported it successfully into CUPS (1.1.20, Linux Fedora Core 2). In the printer setup utility (printtool) I can see (and set) duplex options: Simplex, Duplex Long/Short Edge. It is, however, it is impossible to change the duplex setting on a per-job basis:
  lpr -o sides=two-sided-long-edge
is ignored if the default setting is set to Simplex.
Any ideas?
regards,
Michal.