Virtual Network trashed after latest Xen update for RHEL 5.5

After applying RHSA-2011:1401-1 all Xen DomUs are dead due to (yet to be resolved) network issues.

I use bridging with two interfaces - so xenbr0 and xenbr1 - after update no xenbr0 and no bootable DomUs. First DomU appears as migrating-XXXXX (where XXXXX is the DomU name) and then, after a long pause, login prompt and (maybe) the migrating DomU with missing interfaces and no other DomUs.

ifconfig shows xenbr1 and no xenbr0.

So:

(1) Beware!

(2) Any suggestions for escaping?

===== Update =====

If you have cloned the network-bridge script when implementing a multi-bridge environment (as described in various texts) then this seems to be the root cause. Copy the post update network-bridge script to be the cloned version and life seems to get better,

+++++Update 2+++++

So how do you extend the virtual networking environment in a safe (update invulnerable) way?