Microsoft has issued a update rollup package to resolve problems related to the backup and restoring of virtual machines in Windows Server 2008 R2. The updates will be provided with Service Pack 1 (SP1), Mirosoft said in KB 975354.
Microsoft detailed the issues that are fixed in this update rollup package:
After you install this hotfix on the Hyper-V server, you must update the Integration Components in the virtual machines. To do this, open the Virtual Machine Connection for the virtual machine in Hyper-V Manager, and then select the Insert Integration Services Setup Disk option on the Action menu.
Reference: KB 975354