Comment 0 for bug 1768352

See https://github.com/mate-desktop/mate-screensaver/issues/155

Lock Screen
Turn off monitor
Turn monitor on
Start typing
Expect to see lock screen on monitor

Actual behaviour
Lock Screen
Turn off monitor
Turn monitor on
Start typing
Expect to see lock screen on monitor

Steps to reproduce the behaviour
adddate() {
   while IFS= read -r line; do
      echo "$(date) $line"
   done
}
killall mate-screensaver
mate-screensaver --no-daemon --debug 2>&1 \
  | adddate > screen.log
Wait 60 seconds
Lock screen (I used Window manager shortcut)
Wait 60 seconds
Power off monitor (soft off)
Wait 60 seconds
Power on monitor
Wait 9 seconds (that's how long it takes monitor to boot)
Can see and use screen/type/etc; it is (effectively) unlocked.

Notes/logs:
mate-screensaver-command -q reports:

after killall mate-screensaver:
Screensaver is not running!
After re-running mate-screensaver:
The screensaver is inactive
The screensaver is not inhibited
After locking (stays this way forever even while using the computer)
The screensaver is active
The screensaver is not inhibited
Same as above, annotated with logs: (attached for ease of reading)
mate-screensaver --no-daemon --debug
mate-screensaver-1.txt

Wait 60 seconds
Lock screen (I used Window manager shortcut)
mate-screensaver-2.txt

Wait 60 seconds
Power off monitor (soft off)
mate-screensaver-3.txt
dmesg-3.txt

Wait 60 seconds
Power on monitor
mate-screensaver-4.txt
dmesg-4.txt

Wait 9 seconds (that's how long it takes monitor to boot)
Can see and use screen/type/etc; it is (effectively) unlocked.
dmesg-5.txt

(there is no dmesg-1.txt or dmesg-2.txt or mate-screensaver-5.txt (blank during that time))

Troubleshooting
This occurred on two machines.

Home Machine
Problem occurred on Ubuntu 16.04 (do not have logs unfortunately)
Unsure what version of mate it was at the time
If relevant
monitor was 2560x1600
Uses nvidia drivers
Upgrading to Ubuntu 18.04 (which upgraded mate to 1.20.0) fixed the problem on home machine.
Work Machine
Problem occurred on Ubuntu 17.10 (mate 1.18) (do not have logs unfortunately)
Upgrading to Ubuntu 18.04 (mate 1.20.0) did NOT fix the problem.
If relevant
monitor is 3840x2160
Problem still occurs if I switch to different resolution
Has no dedicated video card/using intel onboard graphics
monitor is a USB hub.. problem still reproduces if I disconnect the usb cable and have the keyboard connected some other way.
Please let me know what other logs/steps may be useful.

MATE general version
1.20.0

Package version
mate-screensaver 1.20.0-1
See attached
mate-packages.txt
for full list of all mate-related package versions

Linux Distribution
Ubuntu 18.04

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: mate-screensaver 1.20.0-1
ProcVersionSignature: Ubuntu 4.15.0-20.21-generic 4.15.17
Uname: Linux 4.15.0-20-generic x86_64
ApportVersion: 2.20.9-0ubuntu7
Architecture: amd64
CurrentDesktop: MATE
Date: Tue May 1 13:56:54 2018
ExecutablePath: /usr/bin/mate-screensaver
InstallationDate: Installed on 2018-02-22 (67 days ago)
InstallationMedia: Ubuntu-MATE 17.10 "Artful Aardvark" - Release amd64 (20180106)
ProcEnviron:
 XDG_RUNTIME_DIR=<set>
 SHELL=/usr/bin/fish
 LANGUAGE=en_US
 PATH=(custom, user)
 LANG=en_US.UTF-8
SourcePackage: mate-screensaver
UpgradeStatus: No upgrade log present (probably fresh install)