Comment 14 for bug 1124803

Ernie, I can confirm that 12.10 with original network-manager
0.9.6.0 has this problem and it appears during shutdown.

I do not play with unchecking of networking, it is always enabled.

The patch mentioned in the comments fixes the issue for me.
Another option is to install to 12.10 the following packages
for Raring:
libnl-3-200_3.2.16-0ubuntu1_amd64.deb
libnl-genl-3-200_3.2.16-0ubuntu1_amd64.deb
libnl-route-3-200_3.2.16-0ubuntu1_amd64.deb
libnm-glib4_0.9.8.0-0ubuntu2_amd64.deb
libnm-util2_0.9.8.0-0ubuntu2_amd64.deb
network-manager_0.9.8.0-0ubuntu2_amd64.deb

I have tested i686 and x86_64, with updated
network-manager both systems cleanly unmount /.

If you see the problem, please, provide
the list of running processes and files open
for writing when root filesystem is about
to be remounted for readonly.