Description of problem:

When I attempt to run more than 1 guest at a time, I receive the following error
when I attempt to start the second guest: 

virDomainCreate() failed Failed to add tap interface 'vnet0' to bridge 'virbr0'
: Device or resource busy

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

$ rpm -qa | grep virt
libvirt-0.3.3-1.fc8
python-virtinst-0.300.1-1.fc8
virt-manager-0.5.2-1.fc8
virt-viewer-0.0.2-1.fc8
libvirt-python-0.3.3-1.fc8

$ uname -a
Linux dalek 2.6.23-5.fc8 #1 SMP Wed Oct 10 19:25:16 EDT 2007 x86_64 x86_64
x86_64 GNU/Linux

How reproducible:

always

Steps to Reproduce:
1. Install 2 guests with shared networking
2. Start 1st guest
3. Start 2nd guest
  
Actual results:

Second guest does not start

Expected results:

Second guest starts

Additional info:

These are QEMU/KVM guests.

Here's the full backtrace: 

Unable to start virtual machine '<class 'libvirt.libvirtError'>
virDomainCreate() failed Failed to add tap interface 'vnet0' to bridge 'virbr0'
: Device or resource busy
Traceback (most recent call last):
  File "/usr/share/virt-manager/virtManager/console.py", line 520, in control_vm_run
    self.vm.startup()
  File "/usr/share/virt-manager/virtManager/domain.py", line 377, in startup
    self.vm.create()
  File "/usr/lib64/python2.5/site-packages/libvirt.py", line 228, in create
    if ret == -1: raise libvirtError ('virDomainCreate() failed', dom=self)
libvirtError: virDomainCreate() failed Failed to add tap interface 'vnet0' to
bridge 'virbr0' : Device or resource busy
'