I just updated our Compellent array (6.3.10) and started to have this issue of vm's getting corrupted during a powered on storage migration. After applying http://support.microsoft.com/kb/2796995#appliesto Hot fix from MS the issue is resolved.

I am currently running VMM 2012 SP1 and Hyper-V 2012.

I don't understand how it worked before the Compellent update if it was a MS issue but I have had other issues that I know were due to Compellent updates and never was able to get Dell/Compellent support to own it.