libvirt users - Jun 2016 - Problem with USB pass through after switching to Xenial from Trusty

I use a virtual machine for a scanner I have for which the vendor never
updated their driver. I have accessed it for years using a pass through:

     <hostdev mode='subsystem' type='usb'
managed='yes'>
       <source>
         <vendor id='0x055f'/>
         <product id='0x040b'/>
       </source>
     </hostdev>

I brought this over from the old config and although the machine
boots as if it sees it, all I get with an lsusb it that the VM's
usb hub exists.

The scanner is showing on the host machine.

I tried deleting the device and remapping it in virt-manager and then 
restarting
the vm. No joy.

So what has changed, or was there something I may have had to do 4 years
ago to set this up that I have long forgotten? Perhaps some hack in udev
on the host?

I really need access to this scanner... like 4 hours ago!