kscreen does not return to original resolution after "Switch to laptop screen"

Steps to reproduce:
- attach external Full-HD monitor (e.g. via HDMI)
- use kscreen to "Unify outputs" (Fn+F7 on my Lenovo T460p, or using the "Display Configuration" tray applet)
- internal monitor is now down to 1920x1080, showing the same content as the external one
- use kscreen to "Switch to laptop screen"

Expected behavior (seen up to and including Ubuntu 21.04):
- external monitor goes black
- internal monitor returns to native resolution (2560x1440 in my case)

Actual behavior (since Ubuntu 21.10):
- external monitor goes black
- internal monitor stays at 1920x1080

ProblemType: Bug
DistroRelease: Ubuntu 21.10
Package: kscreen 4:5.22.4-0ubuntu1
ProcVersionSignature: Ubuntu 5.11.0-25.27-generic 5.11.22
Uname: Linux 5.11.0-25-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.11-0ubuntu67
Architecture: amd64
CasperMD5CheckResult: unknown
CurrentDesktop: KDE
Date: Tue Aug 10 08:12:05 2021
InstallationDate: Installed on 2016-11-26 (1717 days ago)
InstallationMedia: Kubuntu 16.10 "Yakkety Yak" - Release amd64 (20161012.1)
SourcePackage: kscreen
UpgradeStatus: Upgraded to impish on 2021-08-08 (1 days ago)