I tested the lxde iso on Virtualbox(4.1.2) (running the livecd. I'll install it and check again later) and I found out that when you rightclick on the window of pcmanfm it gets restarted. Updating it solves the problem.
Lxappearance gets me:
** (lxappearance:2438): DEBUG: cursor theme name: DMZ-Black
Segmentation fault
Erasing the /usr/share/icon/default/index.theme I get:
** (lxappearance:10365): DEBUG: cursor theme name: (null)
(lxappearance:10365): GLib-GObject-CRITICAL **: g_object_unref:assertion `G_IS_OBJECT (object)' failed
Segmentation fault
I get the 2 line 8times