libvirt users - Apr 2013 - Unexplained shutdown of VM on upgrade of libvirt package

I am running KVM on Centos 6.3 and am seeing an unexplained shut down of 
two guests. The libvirt package was upgraded to 
libvirt-0.10.2-18.el6_4.4.x86_64 at the time of the shutdown. Only the 
two guests shown below was affected, while 9 others running on the same 
hypervisor were not.

Can some one help me to find the cause please ?

Regards
Chandana


GUEST #1
=======2013-04-10 04:15:02.903+0000: starting up
LC_ALL=C PATH=/sbin:/usr/sbin:/bin:/usr/bin QEMU_AUDIO_DRV=none 
/usr/libexec/qemu-kvm -name guinness-a -S -M rhel6.3.0 -enable-kvm -m 
4471 -smp 2,sockets=2,cores=1,threads=1 -uuid 
894072ba-634c-40a2-9f70-0338d124abc3 -nodefconfig -nodefaults -chardev 
socket,id=charmonitor,path=/var/lib/libvirt/qemu/guinness-a.monitor,server,nowait
-mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc 
-no-shutdown -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 -drive 
file=/var/lib/libvirt/images/guinness-a.img,if=none,id=drive-ide0-0-0,format=raw
-device 
ide-drive,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0,bootindex=1 
-netdev tap,fd=28,id=hostnet0 -device 
e1000,netdev=hostnet0,id=net0,mac=54:52:00:98:7f:cc,bus=pci.0,addr=0x3 
-netdev tap,fd=33,id=hostnet1 -device 
e1000,netdev=hostnet1,id=net1,mac=54:52:00:c4:d4:fd,bus=pci.0,addr=0x5 
-netdev tap,fd=34,id=hostnet2 -device 
e1000,netdev=hostnet2,id=net2,mac=54:52:00:a3:33:24,bus=pci.0,addr=0x6 
-chardev pty,id=charserial0 -device 
isa-serial,chardev=charserial0,id=serial0 -vnc 127.0.0.1:1 -vga cirrus 
-device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x4
char device redirected to /dev/pts/11
2013-04-19 01:31:23.502+0000: shutting down
qemu: terminating on signal 15 from pid 12852

GUEST #2
=======2013-03-24 22:30:36.881+0000: starting up
LC_ALL=C PATH=/sbin:/usr/sbin:/bin:/usr/bin QEMU_AUDIO_DRV=none 
/usr/libexec/qemu-kvm -name singha-a -S -M rhel6.3.0 -enable-kvm -m 2048 
-smp 2,sockets=2,cores=1,threads=1 -uuid 
52761f28-8f8d-4d79-a9c0-fd5222502cf4 -nodefconfig -nodefaults -chardev 
socket,id=charmonitor,path=/var/lib/libvirt/qemu/singha-a.monitor,server,nowait 
-mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc 
-no-shutdown -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 -drive 
file=/var/lib/libvirt/images/singha-a.img,if=none,id=drive-ide0-0-0,format=raw 
-device 
ide-drive,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0,bootindex=1 
-netdev tap,fd=32,id=hostnet0 -device 
e1000,netdev=hostnet0,id=net0,mac=54:52:00:2c:75:26,bus=pci.0,addr=0x3 
-netdev tap,fd=33,id=hostnet1 -device 
e1000,netdev=hostnet1,id=net1,mac=54:52:00:b3:80:dd,bus=pci.0,addr=0x5 
-netdev tap,fd=34,id=hostnet2 -device 
e1000,netdev=hostnet2,id=net2,mac=54:52:00:e6:aa:a2,bus=pci.0,addr=0x6 
-chardev pty,id=charserial0 -device 
isa-serial,chardev=charserial0,id=serial0 -vnc 127.0.0.1:0 -vga cirrus 
-device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x4
char device redirected to /dev/pts/5
2013-04-19 01:31:23.515+0000: shutting down
qemu: terminating on signal 15 from pid 12852


PID 12582 is the libvirtd daemon, and I see this in the libvirtd log:

2013-04-19 01:31:23.492+0000: 13039: info : libvirt version: 0.10.2, 
package: 18.el6_4.4 (CentOS BuildSystem <http://bugs.centos.org>, 
2013-04-18-16:13:45, c6b7.bsys.dev.centos.org)
2013-04-19 01:31:23.492+0000: 13039: error : 
virSecuritySELinuxReserveSecurityLabel:676 : internal error MCS level 
for existing domain label  already reserved
2013-04-19 01:31:23.515+0000: 13035: error : 
virSecuritySELinuxReserveSecurityLabel:676 : internal error MCS level 
for existing domain label  already reserved