Here are 2 known issues as advised by the Microsoft Product Group. I have not encountered it yet, but hope it helps someone that has...
- Virtual machine enters a paused state or a CSV volume goes offline when you try to create a backup of he virtual machine on a Windows Server 2012-based failover cluster. A hotfix is available for this condition at http://support.microsoft.com/kb/2799728
- Managing Hyper-V hosts using Virtual Machine Manager fails after installing WMF 3.0 (KB 2795043). The hotfix for this specific condition is documented in KB 2781512, available at the following location: http://support.microsoft.com/kb/2781512