The guest VMs do not connect to the internet via default NAT setting when created on raring desktop hosts

The VMs created on a raring desktop host machine fail to connect to the internet whilst being set to the default NAT settings. The guest VMs complain of failed connectivity. The following error message was observed in the host syslog.
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Jan 15 14:03:52 ubuntu-Macmini NetworkManager[957]: <warn> /sys/devices/virtual/net/vnet0: couldn't determine device driver; ignoring...
Jan 15 14:03:52 ubuntu-Macmini NetworkManager[957]: SCPlugin-Ifupdown: devices added (path: /sys/devices/virtual/net/vnet0, iface: vnet0)
Jan 15 14:03:52 ubuntu-Macmini NetworkManager[957]: SCPlugin-Ifupdown: device added (path: /sys/devices/virtual/net/vnet0, iface: vnet0): no ifupdown configuration found.
Jan 15 14:03:52 ubuntu-Macmini kernel: [ 3925.005518] device vnet0 entered promiscuous mode
Jan 15 14:03:52 ubuntu-Macmini NetworkManager[957]: <info> (virbr0): carrier now ON (device state 30)
Jan 15 14:03:52 ubuntu-Macmini kernel: [ 3925.009671] virbr0: topology change detected, propagating
Jan 15 14:03:52 ubuntu-Macmini kernel: [ 3925.009685] virbr0: port 1(vnet0) entered forwarding state
Jan 15 14:03:52 ubuntu-Macmini kernel: [ 3925.009708] virbr0: port 1(vnet0) entered forwarding state
Jan 15 14:03:53 ubuntu-Macmini avahi-daemon[949]: Joining mDNS multicast group on interface vnet0.IPv6 with address fe80::fc54:ff:fe86:20f2.
Jan 15 14:03:53 ubuntu-Macmini avahi-daemon[949]: New relevant interface vnet0.IPv6 for mDNS.
Jan 15 14:03:53 ubuntu-Macmini avahi-daemon[949]: Registering new address record for fe80::fc54:ff:fe86:20f2 on vnet0.*.
Jan 15 14:04:06 ubuntu-Macmini dnsmasq-dhcp[1336]: DHCP packet received on virbr0 which has no address
Jan 15 14:05:07 dnsmasq-dhcp[1336]: last message repeated 8 times
Jan 15 14:06:08 dnsmasq-dhcp[1336]: last message repeated 7 times
Jan 15 14:07:12 dnsmasq-dhcp[1336]: last message repeated 6 times
Jan 15 14:07:12 ubuntu-Macmini dnsmasq-dhcp[1336]: DHCP packet received on virbr0 which has no address
Jan 15 14:12:15 ubuntu-Macmini dnsmasq-dhcp[1336]: DHCP packet received on virbr0 which has no address
Jan 15 14:13:22 dnsmasq-dhcp[1336]: last message repeated 9 times

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1. Install raring desktop hardware
2. Install kvm, virt-manager and add user to the libvirtd group and log off/log on back (or reboot)
3. Create any desktop VM using the above
4. It could be noticed during and after the VM creation that the guest VM can not connect to the internet ( unless the HOST is rebooted after the VM creation)

This issue does not occur on quantal/precise hosts with any guest VMs
But reproducible with any desktop VMs on Raring HOST

ProblemType: Bug
DistroRelease: Ubuntu 13.04
Package: virt-manager 0.9.4-2ubuntu1
ProcVersionSignature: Ubuntu 3.7.0-7.15-generic 3.7.0
Uname: Linux 3.7.0-7-generic x86_64
ApportVersion: 2.8-0ubuntu1
Architecture: amd64
Date: Tue Jan 15 14:06:35 2013
InstallationDate: Installed on 2013-01-09 (5 days ago)
InstallationMedia: Ubuntu 13.04 "Raring Ringtail" - Alpha amd64+mac (20130109)
MarkForUpload: True
PackageArchitecture: all
SourcePackage: virt-manager
UpgradeStatus: No upgrade log present (probably fresh install)