Screen never locks when inactive

[Cerin]

The "Brightness & Lock" dialog reports that my screen should turn off when inactive for 5 minutes, and it should require my password to unlock, but this never happens. On a fresh install of 14.04, I've left it idle for over an hour and the desktop remains visible and unlocked.

If I press ctrl+alt+l, the screen locks, however, I would expect this to happen automatically according to the "Brightness & Lock" dialog.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: gnome-screensaver 3.6.1-0ubuntu13
ProcVersionSignature: Ubuntu 3.19.0-31.36~14.04.1-generic 3.19.8-ckt7
Uname: Linux 3.19.0-31-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.16
Architecture: amd64
CurrentDesktop: GNOME
Date: Sat Oct 31 14:15:13 2015
GnomeSessionIdleInhibited: No
GnomeSessionInhibitors: 1: AppId = gedit, Flags = 1, Reason = There are unsaved documents
GsettingsGnomeSession:
 org.gnome.desktop.session session-name 'ubuntu'
 org.gnome.desktop.session idle-delay uint32 300
InstallationDate: Installed on 2015-10-20 (10 days ago)
InstallationMedia: Ubuntu 14.04.3 LTS "Trusty Tahr" - Beta amd64 (20150805)
SourcePackage: gnome-screensaver
UpgradeStatus: No upgrade log present (probably fresh install)

[Cerin (chrisspen)]

According to this thread:

http://askubuntu.com/questions/459840/lock-screen-not-working-14-04

this problem is likely due to a bug in gnome-screensaver, in that the 14.04 package does not configure it to run at startup.