Yay, finally there's a new version that fixes all bugs I noticed with xfce4-power-manager: 1.4.0-2
The LidSwitch-Lock-option in the power manager is now working (set HandleLidSwitch in /etc/systemd/logind.conf to ignore), there's a finacy new panel icon and a new settings dialogue.
It's very relieving to have these functions working again.
# Edit: Okay, 1 bug still exists: The screen is not being locked when restarting from suspending.