The USB keyboard is not working with sys-net as the USB qube. I am not quite sure, but i think it did not work when i used a dedicated sys-usb qube either.
I get the following qrexec notifications when plugging in:
Denied **qubes.InputKeyboard** from **sys-net** to **dom0**
This message is displayed 3-4 times simultaneously.
A USB mouse is working just fine.