C2722DE, KVM doesn't disconnect screen when switching

I have my C2722DE monitor set up with a Surface laptop on the USB-C input, and a desktop PC using HDMI and USB-B ports.

On the Surface I have set up the display to extend from the Surface screen to the C2722DE monitor, and it works just fine.

However, if I switch inputs to the desktop PC, the Surface doesn't see that the screen has been disconnected, and still thinks that it has two monitors. Therefore my apps open on this (now) invisible second monitor.

If I unplug the USB-C cable from the Surface, it recognizes that the screen has gone away and adjusts accordingly.

The KVM should be disconnecting the screen from USB-C when switching to a different input.