[CentOS] Kernel panic when adding partitioned virtio disk

I have a cloned kvm (that I can now get started following a shutdown
and reboot of the hypervisor host). When it starts with its original
virtio disk there is no problem.  If I create a virtio disk and add it
via virt-manager it also boots without issue, although one cannot see
the new 'physical' disk.  If I shutodwon the kvm guest, partition the
new virtio disk, and reboot the guest then I see this:

Kernel panic - not syncing: Attempted to kill init!
Pid: 1, comm: init Not tainted 2.6.32-504.12.2.el6.x86_64 #1

Call Trace:
 [ffffffff8152933c] ? panic+0xa7/0x16f
 [ffffffff8107a5f2] ? do_exit+0x862/0x870
 [ffffffff8118fa25] ? fput+0x25/0x30
 [ffffffff8107a658] ? do_group-exit+0x58/0xd0
 [ffffffff8107a6e7] ? sys_exit_group+0x17/0x20
 [ffffffff8100b072] ? system_call_fastpath+0x16/0x1b

Does anyone have any idea what partitioning does to cause this
behaviour?  I have deleted and recreated the virtio disk several times
with differing sizes and it always comes down to whether or not the
disk is partitioned.

I have added virtio disks to other kvm guests in the same fashion many
times and have never run into this.

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