The following fix is from:

https://bbs.archlinux.org/viewtopic.php?id=151786 

I managed to kluge something that works. However, I am not all that sure where the problem originally comes from. I have a suspicion (without any real foundation) it may be a threading problem related to this:

https://mail.gnome.org/archives/gtk-app … 00073.html

Anyway, here is how I got it working (developers may want to fix it some other more elegant way)

Edit the source code in openbox-3.5.0/openbox/openbox.c 

so that the ob_exit function becomes:

void ob_exit(gint code)
{
     exitcode = code;
     g_main_loop_unref(ob_main_loop);
     exit(0);
}

The WM will now exit when you ask it to. This is not likely the best solution, but better than kill -9, at least until the real openbox guys do a real fix.