duplex printing in OpenSolaris

For some time I had duplex printing in my OpenSolaris installation.
But since some time, the printing on HP P3005 was not duplex anymore. Just only
single sided.

The printers are discovered with the SMF-Service
svc:/network/device-discovery/printers:snmp
After looking up the config with
bash-3.2$ lpstat -l -p HP_LaserJet_P3005
printer HP_LaserJet_P3005 idle. enabled since Tue May 26 07:50:48 2009. available.
Form mounted:
Content types: application/postscript
Description: Hewlett-Packard LaserJet P3005
Printer types: unknown
Connection: direct
Interface: /usr/lib/lp/model/uri
PPD: /usr/share/ppd/SUNWfoomatic/HP/HP-LaserJet_P3005_Postscript.ppd.gz
After fault: continue
Users allowed:
(all)
Forms allowed:
(none)
Media supported:
Letter
HalfLetter
Executive
Legal
A4
A5
A6
B5
B6
w558h774
w553h765
w522h737
w612h936
DoublePostcard
Postcard
w612h935
Env10
EnvMonarch
EnvDL
EnvC5
EnvISOB5
Banner page never printed
Character sets:
(none)
Default pitch:
Default page size:
Default port setting:
Options: serial=LLADDR-001E0B1A6B8E
Some time ago I copied there my own PPD file which was from a Solaris 10 SPARC
machine, where the printer is accessed via CUPS.
CUPS had there the duplex unit configured.

So I set the ppd to the new one with

lpadmin -p HP_LaserJet_P3005 -n /usr/share/ppd/SUNWfoomatic/HP/HP-LaserJet_P3005_ewer.ppd.gz
and duplex worked again.
But what I'm missing is the possibility to change the duplex settings in the print dialog or globally.
As I would say, there should be something like a detection mechanism for the duplex unit, but
it doesn't seem to work.