The Global Drive auto-mount feature has been deprecated due to the following Microsoft KB article.
The article says that services mounting drive letters are no longer supported by Microsoft and may act unpredictably. The experience other users have had is that if the connection to the OpenAFS CIFS/SMB server is terminated by the Windows CIFS client, the drive mapping may not be re-established until the machine is rebooted.
OpenAFS supports UNC paths and whenever possible applications should be modified to use UNC form \\AFS\<cellname>\<path> instead of drive letters.
Another problem with service mounted drive letters is that the drives are reported as local disk devices and cannot be resolved as being mapped to the \\AFS name space. As a result, AFS path ioctl operations will fail. The fs.exe and symlink.exe command line tools and the AFS Explorer Shell extension will not operate on service mounted drive letters.