Windows 10 1909, virtio input, QXL/Spice: installing and starting vdservice breaks host mouse

(originally reported at https://github.com/virtio-win/kvm-guest-drivers-windows/issues/438, redirected here)

• Windows 10 1909
• input: virtio keyboard/tablet + PS/2 keyboard/mouse (+ a single Logitech Unifying receiver in passthrough with no devices connected)
• video: QXL/Spice (+ a single NVIDIA GPU in passthrough with no displays connected)
• libvirt + virt-manager

Installing virtio-win guest tools via the installer provided on the release iso (virtio-win-gt-x64.exe) and starting vdservice immediately breaks virtio mouse (the cursor does not disappear, presumably it's drawn by the host, but any mouse actions do not have any effect on the guest). Stopping vdservice immediately fixes the issue, but reopening the Spice session or restarting the guest doesn't.

I can provide any logs or debug output if you point me towards it.