A new update has been released to improve the behavior of Hyper-V while clustered.
"This update incorporates changes in the way that the Windows Server 2008 Failover Cluster Management console functions for the Hyper-V role. These changes provide increased functionality and virtual machine controls that are consistent with the Hyper-V Manager console. This update changes the Failover Cluster Management console (the Cluadmin.msc file) and the server components of the failover cluster. If this update is installed on one node, it should be installed on all nodes of a Windows Server 2008 failover cluster. It may be installed on one node at a time. However, we recommend having all the nodes updated in a reasonable time. You may experience errors on a Failover Cluster Manager that has not been updated to a failover cluster that has had this update applied. These errors occur because of differences between the non-updated Cluadmin.msc file and the updated failover cluster."
Be sure to review the following technical article to learn about the changes and get the update (there's a link at the top of the KB) :
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How can I download the hotfix file for x64
You can download it here through the new Online Hotfix Submission process : http://support.microsoft.com/hotfix/KBHotfix.aspx?kbnum=951308&kbln=en-us
It's quite quick to get hotfixes now !