xscreensaver-command -lock finishes before desktop is invisible

EDIT: Now if it is generally so that when you lock by xscreensaver before suspending, suspending happens only after fading has completed, I withdraw this bug report.

Steps to reproduce
1. Run 'xscreensaver-demo -prefs', activate the daemon, if requested
2. Ensure that "Fade to Black when Blanking" is set up with some non-zero duration.
3. in terminal, run
xscreensaver-command -lock </dev/null && paplay /usr/share/sounds/freedesktop/stereo/bell.oga

Result: The bell sound is played immediately.
Expected: play the sound after blanking is ready
This is regression from (X)ubuntu 18.04, i.e. xscreensaver 5.36-1ubuntu1.

I found a workaround that seems to work at least in Xubuntu 20.04 with certain hardware:
In step 3, run
xscreensaver-command -lock </dev/null && xset dpms force off && paplay /usr/share/sounds/freedesktop/stereo/bell.oga

In that xset command finished only after xscreensaver has finished fading to black.

On another hardware this works, too:

xscreensaver-command -lock </dev/null && xset q >/dev/null && paplay /usr/share/sounds/freedesktop/stereo/bell.oga

ProblemType: Bug
DistroRelease: Ubuntu 19.10
Package: xscreensaver 5.42+dfsg1-1ubuntu1
ProcVersionSignature: Ubuntu 5.3.0-24.26-generic 5.3.10
Uname: Linux 5.3.0-24-generic x86_64
ApportVersion: 2.20.11-0ubuntu8.2
Architecture: amd64
CurrentDesktop: XFCE
Date: Wed Jan 1 15:36:35 2020
InstallationDate: Installed on 2019-12-05 (26 days ago)
InstallationMedia: Xubuntu 19.10 "Eoan Ermine" - Release amd64 (20191017)
SourcePackage: xscreensaver
UpgradeStatus: No upgrade log present (probably fresh install)