Comment 10 for bug 1555237

It doesn't seem like the screensaver really is properly disabled during upgrades, at least looking very naively at what happens during the upgrade -- if I go out of my way to disable it, I got the screen to completely freeze (but at least everything did not crash down to lightdm).

FWIW, I've managed to somewhat make sure the issues were in one of this set for upgrade:
The following packages will be REMOVED:
  gnome-system-monitor libatkmm-1.6-1 libcairomm-1.0-1 libglibmm-2.4-1c2a
  libgtkmm-3.0-1 libmetacity-private0a libpangomm-1.4-1 libsigc++-2.0-0c2a
  overlay-scrollbar-gtk3
The following NEW packages will be installed:
  adwaita-icon-theme gcc-5-base jayatana libappstream-glib8
  libboost-filesystem1.58.0 libboost-system1.58.0 libcolord2 libgcab-1.0-0
  libgcrypt20 libglew1.13 libglewmx1.13 libglibmm-2.4-1v5
  libgnome-desktop-3-12 libgtop-2.0-10 libmetacity-private3a libmirclient9
  libmircommon5 libmirprotobuf3 libprotobuf-lite9v5 libprotobuf9v5
  libsigc++-2.0-0v5 libsystemd0 libyaml-0-2 session-shortcuts unity-schemas
The following packages will be upgraded:
  bamfdaemon compiz-core compiz-gnome compiz-plugins-default fontconfig-config
  gnome-accessibility-themes gnome-desktop3-data indicator-appmenu libatk1.0-0
  libatk1.0-data libbamf3-2 libcairo2 libcompizconfig0 libdecoration0
  libfontconfig1 libgail-3-0 libgpg-error0 libgtk-3-0 libgtk-3-common
  libgtop2-common libharfbuzz0b liblcms2-2 libnux-4.0-0 libnux-4.0-common
  libpango-1.0-0 libpango1.0-0 libpangocairo-1.0-0 libpangoft2-1.0-0
  libpangoxft-1.0-0 libsoup2.4-1 libstdc++6 libunity-core-6.0-9
  libunity-protocol-private0 libunity9 libwayland-client0 libwayland-cursor0
  libxkbcommon0 libxrandr2 metacity-common overlay-scrollbar ubuntu-desktop
  unity unity-services
43 upgraded, 25 newly installed, 9 to remove and 1262 not upgraded.
Need to get 17.9 MB of archives.
After this operation, 12.2 MB of additional disk space will be used.

It certainly still points to an issue in compiz and needs further debugging, but I'll let Eleni deal with it and focus on the screensaver bits in u-r-u, at least to make sure it does disable the screensaver correctly and that I was just mistaken.