Some clients still redirecting folders to old server after GPO has been changed

Recently I moved all users' redirected My Documents folders from one server to another.  After backing everything up I changed the file path in the GPO.  When the users logged on their files were copied over to the new server exactly as planned.  After about a week of smooth sailing I took the old share offline.

Now (about a week after taking the old share offline) some users started to complain of not being able to save their documents.  In all of these cases their My Documents folders are redirecting back to the old server.  There are no entries in the Event Log regarding any errors applying the GPO.

I removed one computer from the domain, rebooted and logged in to the local administrator account.  At that point it attempted to sync with the old server.

What could be causing these machines to revert to the old server?  It is only happening on about 5 machines out of 70 or so.