You should be aware that Windows Server 2012 introduces changes to the application transaction log and BackupComplete in Hyper-V VSS.
The following changes to Hyper-V VSS backups are introduced in Windows Server 2012:
The Hyper-V VSS integration components call BackupComplete inside the virtual machine after the VSS requestor (for example, SnapManager for Hyper-V) that is running on the Hyper-V parent calls BackupComplete.