Upstream fix proposed:
https://www.redhat.com/archives/libvir-list/2012-December/msg01266.html

In POST:
http://post-office.corp.redhat.com/archives/rhvirt-patches/2012-December/msg00575.html

verify with build:
libvirt-0.10.2-14.el6.x86_64
qemu-kvm-rhev-0.12.1.2-2.348.el6.x86_64

step:
# vgcreate vgtest1 /dev/mapper/1IET_00010001
# lvcreate -n lvbaseimg1 -L 1G vgtest1
# lvcreate -n lvbaseimg2 -L 1G vgtest1
# lvcreate -n lvleafimg1 -L 1G vgtest1
# lvcreate -n lvleafimg2 -L 1G vgtest1
# qemu-img create -f qcow2 -F raw -b /dev/vg_virt/lvbaseimg1 /dev/vg_virt/lvleafimg1
# qemu-img create -f qcow2 -F raw -b /dev/vg_virt/lvbaseimg2 /dev/vg_virt/lvleafimg2
# cat > vm1.xml <<EOF
<domain type="kvm">
  <name>vm1</name>
  <memory>131072</memory>
  <devices>
    <disk device="disk" type="block">
      <source dev="/dev/vg_virt/lvleafimg1"/>
      <target bus="ide" dev="hda"/>
      <driver name="qemu" type="qcow2"/>
    </disk>
  </devices>
  <os>
    <type arch="x86_64" machine="pc">hvm</type>
  </os>
</domain>
EOF

# for i in /dev/vg_virt/lv*; do chgrp -v qemu $(readlink -f $i); done

#virsh create vm1.xml

# virsh blockcopy --shallow --reuse-external --wait vm1 /dev/vg_virt/lvleafimg1 /dev/vg_virt/lvleafimg2

Now in mirroring phase

#for i in /dev/vg_virt/lv*; do ls -Z $(readlink -f $i); done
brw-rw----. qemu qemu system_u:object_r:virt_content_t:s0 /dev/dm-0
brw-rw----. qemu qemu system_u:object_r:virt_content_t:s0 /dev/dm-1
brw-rw----. qemu qemu unconfined_u:object_r:svirt_image_t:s0:c256,c359 /dev/dm-2
brw-rw----. root root system_u:object_r:fixed_disk_device_t:s0 /dev/dm-3


make sure blockjob in phase two
#virsh blockjob --info vm1 /dev/vg_virt/lvleafimg1
Block Copy: [100 %]

# virsh blockjob --pivot vm1 /dev/vg_virt/lvleafimg1

no error display
# for i in /dev/vg_virt/lv*; do ls -Z $(readlink -f $i); done
brw-rw----. qemu qemu system_u:object_r:virt_content_t:s0 /dev/dm-0
brw-rw----. qemu qemu system_u:object_r:virt_content_t:s0 /dev/dm-1
brw-rw----. qemu qemu unconfined_u:object_r:svirt_image_t:s0:c538,c961 /dev/dm-2
brw-rw----. qemu qemu unconfined_u:object_r:svirt_image_t:s0:c538,c961 /dev/dm-3

#virsh dumpxml vm1
.....
<disk type='block' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source dev='/dev/vg_virt/lvleafimg2'/>
      <target dev='hda' bus='ide'/>
.....

worked as expect. verification passed.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

http://rhn.redhat.com/errata/RHSA-2013-0276.html