I'm working on a upgrade of Hyper-V 2008R2 cluster to Hyper-V 2012 cluster. I am using the "migrate roles" feature of failover clustering to migrate the CSV's and VM's. The wizard ask to which switch the VMs need to be connected on the target cluster. All VMs with network adapters can be started in the new cluster without any issues. If you look at the XML file of the migrated VMs with normal network adapters, a new XML has been generated in the proper 2012 format. However, all VM's with a legacy network adapter fail to start. Also there is no migrated XML file in the VM directory. It is impossible to check or adjust the settings of the migrated VMs with legacy network adapters using the failover clustering console.
I have reproduced the issue in my lab several times, and it seems like a bug.
There are several workarounds, but I am looking for a real solution.