Choosing "Shared physical device" in virt-manager

[Alvin]

Relevancy to Kubuntu: I want to run some virtual Ubuntu servers with kubuntu-
desktop for XDMCP.
There is no ubuntu-server-users mailinglist, so I'm asking here.

The libvirt setup went fine. I was even able to define LVM storage pools and 
all. The only thing not going well is the bridged networking.

Bridging on the host has to be configured manually, and it works. This is the 
proof (I disabled the default network):
alvin at virthost02:~$ brctl show
bridge name     bridge id               STP enabled     interfaces
br0             8000.00215a51b093       no              eth0

'virthost02' is a clean, headless ubuntu-server.
Using virt-manager over qemu+ssh on my Kubuntu workstation, I can create a new 
virtual machine, but I'm stuck at the "Connect to host network" window.
It gives me two options: using the disabled default network, or a grayed out 
"Shared physical device" option. That one is the bridge, but it is not 
recognized by virt-manager (or libvirtd?).

Is there someone who knows how I can make virt-manager see the bridge?