The Global DriveAuto-mount feature has been deprecated due to the following Microsoft KB article.

http://msdn.microsoft.com/library/en-us/dllproc/base/services_and_redirected_drives.asp

It 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 of \\AFS\<cellname>\<path> instead of drive letters.