I have the same problem with my Officejet Pro 8000:
I'm running PCLinuxOS 2010 (Gnome version) with HPLIP 3.10.5
I have all duplexing options turned on in the HP Device Manager but no matter which application I try, there is NO option for duplex printing. I've tried the "A4 AutoDuplex" suggestion but that doesn't make any difference.
I have the same problem with my Officejet Pro 8000:
I'm running PCLinuxOS 2010 (Gnome version) with HPLIP 3.10.5
I have all duplexing options turned on in the HP Device Manager but no matter which application I try, there is NO option for duplex printing. I've tried the "A4 AutoDuplex" suggestion but that doesn't make any difference.