I think this may be an upstream issue. On a whim, I updated a faithful old Thinkpad running Debian Squeeze to Wheezy, and the same issue occurs there - when I have an NFS mount, it does not shut down, but when I unmount it before shutting down, the machine powers off correctly. I did not go through all the "set -x" routine to confirm, but the behaviour is exactly the same. This worked perfectly under Squeeze, the same as it has worked under Natty.
I think this may be an upstream issue. On a whim, I updated a faithful old Thinkpad running Debian Squeeze to Wheezy, and the same issue occurs there - when I have an NFS mount, it does not shut down, but when I unmount it before shutting down, the machine powers off correctly. I did not go through all the "set -x" routine to confirm, but the behaviour is exactly the same. This worked perfectly under Squeeze, the same as it has worked under Natty.
S