Suspend button not working with screen is locked by xsecurelock

Submitted by Egon

Link to original bug (#12703)

Description

With the following settings in /etc/systemd/logind.conf

SuspendKeyIgnoreInhibited=yes

one can suspend by pressing the suspend button when the screen is locked by xsecurelock.

If xfce4-power-manager is running, then suspend by the suspend button is no longer possible.

However, closing the lid always suspends, with or without xfce4-power-manager.

Why is that?
How to make xfce4-power-manager allow xsecurelock suspending by pressing the suspend button?

Version: 1.4.x