Power manager locks screen but does not show lock-screen

There are circumstances when the power manager locks the screen and suspends the computer, but on wake-up no lock-screen is shown. Nevertheless, the screen is locked and a password has to be entered into the invisible input box.

1. This happens when the display is in 'presentation mode'. On shutting the laptop lid everything proceeds as expected except that on re-opening the lid I can still see the display as it was, no mouse or key-presses work, and the screen is locked until I enter the unlock password in a dialogue box that is not visible.

2. If working with an external display with the laptop lid shut, then if I unplug the external monitor a similar thing happens. When I open the laptop lid I get a locked screen but the original display is still visible.

For me this is no more than a minor nuisance, but it would appear to be a security issue in that possibly private information is visible to anyone who opens the laptop lid.

ProblemType: Bug
DistroRelease: Ubuntu 22.04
Package: xfce4-power-manager 4.16.0-1
ProcVersionSignature: Ubuntu 5.15.0-58.64-generic 5.15.74
Uname: Linux 5.15.0-58-generic x86_64
ApportVersion: 2.20.11-0ubuntu82.3
Architecture: amd64
CasperMD5CheckResult: unknown
CurrentDesktop: XFCE
Date: Wed Feb 15 11:38:32 2023
InstallationDate: Installed on 2020-09-17 (880 days ago)
InstallationMedia: Xubuntu 20.04 LTS "Focal Fossa" - Release amd64 (20200423)
SourcePackage: xfce4-power-manager
UpgradeStatus: Upgraded to jammy on 2022-10-30 (107 days ago)