Hi.

Unfortunately the screen then can only be unblanked with Alt+Print+K.

There is a syslog message related to this:
mate-screensave[8614]: Failed to get session presence proxy: Could not get owner of name 'org.gnome.SessionManager': no such name

Currently the following screensaver packages are installed:

jo@backspace:~$ aptitude search screensaver | grep "^i"
i  libkscreensaver5 - library of the KDE Screensaver system
i A mate-screensaver - MATE-Bildschirmschoner und -sperrer
i A mate-screensaver-common - MATE-Bildschirmschoner und -sperrer (gemeinsame Dateien)
i A xscreensaver - Bildschirmschoner-Daemon und -Frontend für X11
i A xscreensaver-data - Bildschirmschoner-Module für Bildschirmschoner-Frontends
i  xscreensaver-data-extra - Extra screen saver modules for screensaver frontends
i A xscreensaver-gl - GL(Mesa) screen saver modules for screensaver frontends
i  xscreensaver-gl-extra - Extra GL(Mesa) screen saver modules for screensaver frontends
i  xscreensaver-screensaver-bsod - BSOD screen saver module from XScreenSaver

Sincerely,
Joachim

I am not able to reproduce this issue on stable and sid. If we set the idle time, screensaver appears as expected.

As the issue is very old (v1.16.1-1), please consider closing this bug.