I just noticed a newer pcmanfm in the raring ringtail repositories, so I installed it to give it a try. It is version 1.1.0-0ubuntu1 and so far it is working good in Lubuntu 12.10 after setting the wallpaper from command line.

https://launchpad.net/ubuntu/+source/pcmanfm
or
http://packages.ubuntu.com/search?ke...ng&section=all