Description of problem:
When add one network on guest hotplug with virt-manager, in the /etc/libvirt/qemu/guest.xml there will be two parts of network with same mac and source. But in the guest only one can be detected and used. If you hotunplug it and reboot the vm, the network device will appear again.

# cat /etc/libvirt/qemu/guest.xml
<domain type='kvm'>
  <name>cd-inst</name>
  <uuid>aaaa0000-bbbb-1111-cccc-2222dddd3333</uuid>
  <memory>2097152</memory>
  <currentMemory>2097152</currentMemory>
  <vcpu cpuset='2'>1</vcpu>
  <os>
    <type arch='x86_64' machine='rhel6.0.0'>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/libexec/qemu-kvm</emulator>
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw' cache='none'/>
      <source file='/var/lib/libvirt/images/cd-inst.img'/>
      <target dev='hda' bus='ide'/>
      <address type='drive' controller='0' bus='0' unit='0'/>
    </disk>
    <disk type='block' device='cdrom'>
      <driver name='qemu' type='raw'/>
      <target dev='hdc' bus='ide'/>
      <readonly/>
      <address type='drive' controller='0' bus='1' unit='0'/>
    </disk>
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw'/>
      <source file='/var/lib/libvirt/images/rhel-x86_64.img'/>
      <target dev='hdb' bus='ide'/>
      <address type='drive' controller='0' bus='0' unit='1'/>
    </disk>
    <controller type='ide' index='0'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
    </controller>

    <interface type='network'>
      <mac address='52:54:00:53:34:d8'/>
      <source network='default'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </interface>
    <interface type='network'>
      <mac address='52:54:00:53:34:d8'/>
      <source network='default'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
    </interface>

    <serial type='pty'>
      <target port='0'/>
    </serial>
    <console type='pty'>
      <target port='0'/>
    </console>
    <input type='mouse' bus='ps2'/>
    <graphics type='vnc' port='-1' autoport='yes' keymap='en-us'/>
    <sound model='es1370'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
    </sound>
    <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>



Version-Release number of selected component (if applicable):

virt-manager-0.8.4-7.el6.noarch
libvirt-0.8.1-21.el6.x86_64
kernel-2.6.32-61.el6.x86_64

How reproducible:
100%

Steps to Reproduce:
1.Launch virt-manager: #virt-manager
2.Double-click a vm and click the Run button in the Virtual Machine Details window.
3.Click the Hardware tab.
4.Click Add Hardware button
5.Select Network in Hardware type droplist and click Forward.
6.Select Vitual network, set fixed MAC,and select default in Device Model droplist, then click Forward button.
7.Click Finish button.
8.Select the NIC you just added then click Remove button.
9.Reboot the vm and check Hardware tab.
  
Actual results:
There is still one network device which is you just delete

Expected results:
There is no network device

Additional info: