U2722DE, stop Ethernet from switching away from USB-C

I have a supremely annoying problem with my Dell U2722DE monitor. Every time I switch the keyboard, video & mouse away from my laptop to my desktop PC, the laptop loses its network connection, and this causes my VPN to drop and/or any downloads to fail!

The problem seems to be that the KVM function is switching the Ethernet away from the USB-C connection to the laptop, along with the keyboard, video and mouse signals.

It’s an really annoying quirk that spoils an otherwise excellent monitor.