On a side note, I do believe this is a bug in gnome screensaver. It should have a notion of whether or not it is supposed to be managing screensaving in the user session, and if not then it should respond to DBus clients with an appropriate error if they try to activate it.
Can note that this still happens in Trusty, and since bug #726471 is fixed, this user level workaround now works:
mkdir -p ~/.local/ share/dbus- 1/services share/dbus- 1/services/ org.gnome. ScreenSaver. service gnome.ScreenSav er
cat <<EOF > ~/.local/
[D-BUS Service]
Name=org.
Exec=
EOF
On a side note, I do believe this is a bug in gnome screensaver. It should have a notion of whether or not it is supposed to be managing screensaving in the user session, and if not then it should respond to DBus clients with an appropriate error if they try to activate it.