gnome-screensaver cannot lock the screen

[Tommy_CZ]

gnome-screensaver cannot lock the screen, the ability is disabled in settings and after I click ctrl+alt+L the screen goes black, but I can wake it then without password.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: gnome-screensaver 3.6.1-7ubuntu4
Uname: Linux 4.7.0-040700-generic x86_64
NonfreeKernelModules: nvidia_uvm nvidia_drm nvidia_modeset nvidia
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: amd64
CurrentDesktop: Unity
Date: Wed Aug 24 20:20:24 2016
GnomeSessionIdleInhibited: No
GnomeSessionInhibitors: None
GsettingsGnomeSession:
 org.gnome.desktop.session session-name 'ubuntu'
 org.gnome.desktop.session idle-delay uint32 0
InstallationDate: Installed on 2016-07-26 (29 days ago)
InstallationMedia: Lubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420)
SourcePackage: gnome-screensaver
UpgradeStatus: No upgrade log present (probably fresh install)