I filed a bug-report which got the security team interested they said they got a few other complaints.
Thank you for your report.
We have had another report of something like that happening to another user
on a Lenovo T450s.
Can you please provide some additional information to help us decide what
to do about this issue?
We would like the output of the commands:
xrandr # when external monitor is connected
inxi -G # same thing
apt-cache policy mate-screensaver
gsettings list-recursively | grep -i screensaver
Can you also please investigate your log files for any messages related
to mate-screensaver crashing?
The bug report is at the link below -- but you wont be able to see it because it was marked as a security bug.
thus you can try to email 1769278[ @at@] bugs.launchpad.net and CC this address: etienne.papegnies [@at@] univ-avignon.fr