[libvirt-users] Duplicate USB vendor,product specification

I studying how to attach USB devices to a KVM guest virtual machine using libvirt. Using the "vendor" and "product" to specify the source device seems like a good option since the "bus" and "device" values can change as a device is removed and re-inserted. The question I have is what should I expect to happen if I plug in two identical USB devices - so they have the same vendor/product information? There is nothing in the documentation on libvirt.org to address this case. Thanks. Don Morrison