Upgrade to virtinst0.600.1-1ubuntu3.2  doesn't solve the problem.

# virt-clone -o ubuntu-1204-10G -n omcsvctst01d -f /data/instances/omcsvctst01d.img -d
[Fri, 09 Aug 2013 10:53:33 virt-clone 8084] DEBUG (cli:220) Launched with command line:
/usr/bin/virt-clone -o ubuntu-1204-10G -n omcsvctst01d -f /data/instances/omcsvctst01d.img -d
[Fri, 09 Aug 2013 10:53:33 virt-clone 8084] DEBUG (cli:326) Requesting libvirt URI default
[Fri, 09 Aug 2013 10:53:33 virt-clone 8084] DEBUG (cli:328) Received libvirt URI qemu:///system
[Fri, 09 Aug 2013 10:53:34 virt-clone 8084] DEBUG (CloneManager:399) Validating original guest parameters
[Fri, 09 Aug 2013 10:53:34 virt-clone 8084] DEBUG (CloneManager:408) Original XML:
<domain type='kvm'>
  <name>ubuntu-1204-10G</name>
  <uuid>28538012-f2b4-1fa2-acfc-99c0a35c6a78</uuid>
  <memory>1048576</memory>
  <currentMemory>1048576</currentMemory>
  <memoryBacking>
    <hugepages/>
  </memoryBacking>
  <vcpu>2</vcpu>
  <os>
    <type arch='x86_64' machine='pc-1.0'>hvm</type>
    <boot dev='hd'/>
  </os>
  <features>
    <acpi/>
    <apic/>
    <pae/>
  </features>
  <clock offset='utc'/>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>restart</on_crash>
  <devices>
    <emulator>/usr/bin/kvm</emulator>
    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/data/templates/ubuntu-1204-10G.img'/>
      <target dev='vda' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
    </disk>
    <disk type='file' device='cdrom'>
      <driver name='qemu' type='raw'/>
      <target dev='hdc' bus='ide'/>
      <readonly/>
      <address type='drive' controller='0' bus='1' unit='0'/>
    </disk>
    <controller type='ide' index='0'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
    </controller>
    <interface type='bridge'>
      <mac address='52:54:00:04:c0:4a'/>
      <source bridge='br-828'/>
      <model type='virtio'/>
      <driver name='vhost' txmode='iothread' ioeventfd='on' event_idx='off'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </interface>
    <serial type='pty'>
      <target port='0'/>
    </serial>
    <console type='pty'>
      <target type='serial' port='0'/>
    </console>
    <input type='mouse' bus='ps2'/>
    <graphics type='vnc' port='-1' autoport='yes'/>
    <video>
      <model type='cirrus' vram='9216' heads='1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    </video>
    <memballoon model='virtio'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
    </memballoon>
  </devices>
</domain>

[Fri, 09 Aug 2013 10:53:36 virt-clone 8084] DEBUG (CloneManager:416) Original paths: ['/data/templates/ubuntu-1204-10G.img']
[Fri, 09 Aug 2013 10:53:36 virt-clone 8084] DEBUG (CloneManager:417) Original sizes: [10.0]
[Fri, 09 Aug 2013 10:53:38 virt-clone 8084] DEBUG (VirtualDisk:240) Path '/data/instances' is target for pool 'default'. Creating volume 'omcsvctst01d.img'.
[Fri, 09 Aug 2013 10:53:39 virt-clone 8084] DEBUG (VirtualDisk:240) Path '/data/instances' is target for pool 'default'. Creating volume 'omcsvctst01d.img'.
[Fri, 09 Aug 2013 10:53:39 virt-clone 8084] DEBUG (CloneManager:399) Validating original guest parameters
[Fri, 09 Aug 2013 10:53:39 virt-clone 8084] DEBUG (CloneManager:408) Original XML:
<domain type='kvm'>
  <name>ubuntu-1204-10G</name>
  <uuid>28538012-f2b4-1fa2-acfc-99c0a35c6a78</uuid>
  <memory>1048576</memory>
  <currentMemory>1048576</currentMemory>
  <memoryBacking>
    <hugepages/>
  </memoryBacking>
  <vcpu>2</vcpu>
  <os>
    <type arch='x86_64' machine='pc-1.0'>hvm</type>
    <boot dev='hd'/>
  </os>
  <features>
    <acpi/>
    <apic/>
    <pae/>
  </features>
  <clock offset='utc'/>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>restart</on_crash>
  <devices>
    <emulator>/usr/bin/kvm</emulator>
    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/data/templates/ubuntu-1204-10G.img'/>
      <target dev='vda' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
    </disk>
    <disk type='file' device='cdrom'>
      <driver name='qemu' type='raw'/>
      <target dev='hdc' bus='ide'/>
      <readonly/>
      <address type='drive' controller='0' bus='1' unit='0'/>
    </disk>
    <controller type='ide' index='0'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
    </controller>
    <interface type='bridge'>
      <mac address='52:54:00:04:c0:4a'/>
      <source bridge='br-828'/>
      <model type='virtio'/>
      <driver name='vhost' txmode='iothread' ioeventfd='on' event_idx='off'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </interface>
    <serial type='pty'>
      <target port='0'/>
    </serial>
    <console type='pty'>
      <target type='serial' port='0'/>
    </console>
    <input type='mouse' bus='ps2'/>
    <graphics type='vnc' port='-1' autoport='yes'/>
    <video>
      <model type='cirrus' vram='9216' heads='1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    </video>
    <memballoon model='virtio'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
    </memballoon>
  </devices>
</domain>

[Fri, 09 Aug 2013 10:53:41 virt-clone 8084] DEBUG (CloneManager:416) Original paths: ['/data/templates/ubuntu-1204-10G.img']
[Fri, 09 Aug 2013 10:53:41 virt-clone 8084] DEBUG (CloneManager:417) Original sizes: [10.0]
[Fri, 09 Aug 2013 10:53:41 virt-clone 8084] DEBUG (CloneManager:517) Original guest xml is
<domain type='kvm'>
  <name>ubuntu-1204-10G</name>
  <uuid>28538012-f2b4-1fa2-acfc-99c0a35c6a78</uuid>
  <memory>1048576</memory>
  <currentMemory>1048576</currentMemory>
  <memoryBacking>
    <hugepages/>
  </memoryBacking>
  <vcpu>2</vcpu>
  <os>
    <type arch='x86_64' machine='pc-1.0'>hvm</type>
    <boot dev='hd'/>
  </os>
  <features>
    <acpi/>
    <apic/>
    <pae/>
  </features>
  <clock offset='utc'/>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>restart</on_crash>
  <devices>
    <emulator>/usr/bin/kvm</emulator>
    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/data/templates/ubuntu-1204-10G.img'/>
      <target dev='vda' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
    </disk>
    <disk type='file' device='cdrom'>
      <driver name='qemu' type='raw'/>
      <target dev='hdc' bus='ide'/>
      <readonly/>
      <address type='drive' controller='0' bus='1' unit='0'/>
    </disk>
    <controller type='ide' index='0'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
    </controller>
    <interface type='bridge'>
      <mac address='52:54:00:04:c0:4a'/>
      <source bridge='br-828'/>
      <model type='virtio'/>
      <driver name='vhost' txmode='iothread' ioeventfd='on' event_idx='off'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </interface>
    <serial type='pty'>
      <target port='0'/>
    </serial>
    <console type='pty'>
      <target type='serial' port='0'/>
    </console>
    <input type='mouse' bus='ps2'/>
    <graphics type='vnc' port='-1' autoport='yes'/>
    <video>
      <model type='cirrus' vram='9216' heads='1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    </video>
    <memballoon model='virtio'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
    </memballoon>
  </devices>
</domain>

[Fri, 09 Aug 2013 10:53:41 virt-clone 8084] DEBUG (CloneManager:434) Validating clone parameters.
[Fri, 09 Aug 2013 10:53:41 virt-clone 8084] DEBUG (CloneManager:444) Clone paths: ['/data/instances/omcsvctst01d.img']
[Fri, 09 Aug 2013 10:53:41 virt-clone 8084] DEBUG (CloneManager:520) Clone guest xml is
<domain type="kvm">
  <name>omcsvctst01d</name>
  <uuid>ef6cbdd5-36aa-3698-7360-c29d27666561</uuid>
  <memory>1048576</memory>
  <currentMemory>1048576</currentMemory>
  <memoryBacking>
    <hugepages/>
  </memoryBacking>
  <vcpu>2</vcpu>
  <os>
    <type arch="x86_64" machine="pc-1.0">hvm</type>
    <boot dev="hd"/>
  </os>
  <features>
    <acpi/>
    <apic/>
    <pae/>
  </features>
  <clock offset="utc"/>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>restart</on_crash>
  <devices>
    <emulator>/usr/bin/kvm</emulator>
    <disk type="file" device="disk">
      <driver name="qemu" type="qcow2"/>
      <target dev="vda" bus="virtio"/>
      <address type="pci" domain="0x0000" bus="0x00" slot="0x04" function="0x0"/>
      <source file="/data/instances/omcsvctst01d.img"/>
    </disk>
    <disk type="file" device="cdrom">
      <driver name="qemu" type="raw"/>
      <target dev="hdc" bus="ide"/>
      <readonly/>
      <address type="drive" controller="0" bus="1" unit="0"/>
    </disk>
    <controller type="ide" index="0">
      <address type="pci" domain="0x0000" bus="0x00" slot="0x01" function="0x1"/>
    </controller>
    <interface type="bridge">
      <mac address="52:54:00:35:16:5b"/>
      <source bridge="br-828"/>
      <model type="virtio"/>
      <driver name="vhost" txmode="iothread" ioeventfd="on" event_idx="off"/>
      <address type="pci" domain="0x0000" bus="0x00" slot="0x03" function="0x0"/>
    </interface>
    <serial type="pty">
      <target port="0"/>
    </serial>
    <console type="pty">
      <target type="serial" port="0"/>
    </console>
    <input type="mouse" bus="ps2"/>
    <graphics type="vnc" port="-1" autoport="yes"/>
    <video>
      <model type="cirrus" vram="9216" heads="1"/>
      <address type="pci" domain="0x0000" bus="0x00" slot="0x02" function="0x0"/>
    </video>
    <memballoon model="virtio">
      <address type="pci" domain="0x0000" bus="0x00" slot="0x05" function="0x0"/>
    </memballoon>
  </devices>
</domain>

[Fri, 09 Aug 2013 10:53:41 virt-clone 8084] DEBUG (CloneManager:615) Starting duplicate.
[Fri, 09 Aug 2013 10:53:41 virt-clone 8084] DEBUG (Storage:1195) Creating storage volume 'omcsvctst01d.img' with xml:
<volume>
  <name>omcsvctst01d.img</name>
  <capacity>107</capacity>
  <allocation>0</allocation>
  <target>
    <format type='raw'/>
  </target>
</volume>

Allocating 'omcsvctst01d.img'                                                                                                  |  107 B     02:02     
[Fri, 09 Aug 2013 10:55:44 virt-clone 8084] DEBUG (Storage:1218) Storage volume 'omcsvctst01d.img' install complete.
[Fri, 09 Aug 2013 10:55:46 virt-clone 8084] DEBUG (CloneManager:637) Duplicating finished.
Allocating 'omcsvctst01d.img'                            2098124321% [==============================================] 316 MB/s | 2.1 GB     --:-- ETA 
Clone 'omcsvctst01d' created successfully.
[Fri, 09 Aug 2013 10:55:59 virt-clone 8084] DEBUG (virt-clone:249) end clone

# qemu-img info omcsvctst01d.img
image: omcsvctst01d.img
file format: raw
virtual size: 10G (10737418240 bytes)
disk size: 2.1G

#qemu-img info ubuntu-1204-10G.img 
image: ubuntu-1204-10G.img
file format: qcow2
virtual size: 10G (10737418240 bytes)
disk size: 1.0G
cluster_size: 65536