Duplex Printing with HPLIP 3.13.6 on HP LJ M1536DNF MFP

[sas3]

I use Ubuntu 13.04.
   uname -a
   Linux sas3-c3po 3.8.0-26-generic #38-Ubuntu SMP Mon Jun 17 21:43:33 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux)

I've made sure that the device settings (for HP LJ M1536DNF MFP) all show "Duplexer Installed" and Printer settings show "Long Edge Binding".

To be sure, I followed instructions from here (https://answers.launchpad.net/hplip/+question/227264) -- removed all HP printers, installed the plugins, setup the new queue & device properly (with Duplexer, etc.) and tried again. Printer still prints single sided.

There is no problem with the printer as this was working fine before I installed HPLIP (I had to install HPLIP because another printer -- an M1136 wouldn't print otherwise).

I'm attaching the logfile I created with hp-logcapture. Am also attaching the /etc/hp/hplip.conf (as etc-hp-hplip.conf) and ~/.hplip/hplip.conf (as home-.hplip-hplip.conf).

Ran hp-doctor as advised below. Output is attached as hp-doctor.output (includes stderr output). This appears to be a superset of hp-check, so am not including it separately.