Comment # 2 on bug 961831 from George Anchev

> There is no guarantee that constant bus id and device id are assigned to a
> usb device during device scanning.
> If they changed on host and you start the guest which including the old
> information of usb host device, you will receive the above error message.
> 
> So after rebooting the host, when you saw the above error message, It means
> your usb device got new bus id and device id, Please check it, if this is
> the case, then this's not a bug.

Hm. You are right. The assigned bus is different after reboot.

But then comes the question - how do I use my USB devices without having to
re-add them in the guest after each reboot? I never had to do this in VMWare
Workstation (for example).

> Please file a new bug for this.

Will do.
> 
> BTW, In my test env, If no virt-manager instance exists, then "Create
> Virtual Machines for Xen and KVM" works well, that means after clicking, a
> virt-manager window and a "new VM" window are poped up.
> If there is virt-manager instance already there, then after clicking "Create
> Virtual Machines for Xen and KVM" in YaST, no "new VM" window is poped up.

I don't see any other instances running. I close everything, start YaST and
then try to run "Create
> Virtual Machines for Xen and KVM". Anyway I will describe it again in a new bug report.