The GetVolumePathNameW function does not return the correct mount point path in Windows Vista and in Windows Server 2008
You have a volume mount point on a network share. In Windows Vista or in Windows Server 2008, when you call the GetVolumePathNameW function on the UNC path of the volume mount point to retrieve the specified mount point path, the function returns only the path of the network share. However, you expect the function to return the mount point path.
In Windows XP or Windows Server 2003, the mount path is returned as expected.
For example, you have a network share whose UNC path is \\Server\Share. In the network share, you have a volume mount point that has the UNC path \\Server\Share\MountDrive. When you pass the UNC path \\Server\Share\MountDrive\SubDir to the GetVolumePathNameW function to retrieve the mount point path, the function returns \\Server\Share. In Windows XP and Windows Server 2003, the function returns \\Server\Share\MountDrive.
For more information on this issue, including potential causes, workarounds, and resolutions, see: Microsoft KB Article KB961349.