Bug#825463: gnome-screensaver: gnome screensaver not working

[clayton]

Package: gnome-screensaver
Version: 3.6.1-7+b1
Severity: important

gnome-core installed, gnome-screensaver installed, gdm3 is my default display manager,
screen lock is turned on in gnome settings: nothing happens. The screensaver does not turn on
automatically, nor is there any obvious way to turn it on manually.

-- System Information:
Debian Release: stretch/sid
  APT prefers testing
  APT policy: (990, 'testing'), (700, 'unstable'), (1, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.5.0-2-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages gnome-screensaver depends on:
ii  dbus-x11                   1.10.8-1
ii  gnome-icon-theme           3.12.0-1
ii  gnome-session-bin          3.20.1-2
ii  gsettings-desktop-schemas  3.20.0-3
ii  libc6                      2.22-9
ii  libcairo2                  1.14.6-1+b1
ii  libdbus-1-3                1.10.8-1
ii  libdbus-glib-1-2           0.106-1
ii  libgdk-pixbuf2.0-0         2.34.0-1
ii  libglib2.0-0               2.48.1-1
ii  libgnome-desktop-3-12      3.20.2-1
ii  libgnomekbd8               3.6.0-1
ii  libgtk-3-0                 3.20.4-1
ii  libpam0g                   1.1.8-3.2
ii  libsystemd0                229-6
ii  libx11-6                   2:1.6.3-1
ii  libxext6                   2:1.3.3-1
ii  libxklavier16              5.2.1-1
ii  libxxf86vm1                1:1.1.4-1

Versions of packages gnome-screensaver recommends:
ii  gnome-power-manager   3.20.0-1
ii  libpam-gnome-keyring  3.20.0-1

gnome-screensaver suggests no packages.

-- debconf-show failed