qemu-ga won't start on Windows 8.1 guest

System: Arch Linux, kernel 4.6.2
VM created with virt-manager 1.3.2
qemu version 2.6.0
Windows guest: 8.1, with latest updates (as of now)
Drivers installed from virtio-win iso image (arch package version 0.1.118.2-1)
  in particular: vioserial driver version 62.73.104.11800

I can start the Guest Agent VSS Provider manually, but the Guest Agent itself doesn't come up. When launched from Console, I get the following:

<timestamp>: critical: error opening path
<timestamp>: critical: error opening channel
<timestamp>: critical: failed to create guest agent channel
<timestamp>: critical: failed to initialize guest agent channel

(As possible side effects I have experienced that suspend / resume of the VM only works when I resume, suspend again and resume again. After first resume the VM's screen is frozen and doesn't accept any input. After second resume, all seems to be well.)