Xen users - Jan 2012 - Ubuntu (Pangolin) HVMs become unpingable when migrated back to box where they were created

I have a 2-node cluster running Debian Squeeze as the Dom0 for each of 
the nodes, and Precise Pangolin Ubuntu DomUs.


If I create an HVM instance on one of the Debian nodes and migrate it to 
the 2nd node, all is well. But if I then migrate the HVM back to the 
node on which it had been created, it becomes unavailable on the 
network. A Ping shows it is unavailable. The console hangs for this HVM, 
suggesting the HVM is in kernel panic although I cannot verify this.

I have guessed that there''s a bad housekeeping problem on the 
originating node that somehow causes a conflict with the original, now 
returning HVM, and that this conflict interferes with the netfront 
driver somehow.

Any ideas?