6.6.3 - Editing VM returns error

No matter what I do trying to update the VM returns this error...

I have an USB audio interface which I can't ad from the normal editor, which I can circumvent with adding

    <hostdev mode='subsystem' type='usb' managed='no'>
      <source>
        <vendor id='vendorID'/>
        <product id='productID'/>
      </source>
    </hostdev>

The problem is have not ticked the audio interface (see image), and I'm not even trying to add it. Changing any setting returns creation error...

HOW TO REPRODUCE:

• Create a VM in 6.6.3
• Install and boot with VNC
• shutdown - then edit the VM (not XML)
• For me trying to pass-through a GPU will create the error
  • (though any setting should do it, like adding more cpu cores)
• Click update

>creation error