My screen dos't lock when and Indicator is active

My PC usually locks the screen after 1min. But when I activate the soundmenu, calender or another indicator the PC doesn’t lock the screen. When I remove the cursor and close the indicator menu it sometimes locks the screen immediately and sometimes not.

Ubuntu 12.04 LTS
gnome-screensaver:
  Installiert: 3.4.1-0ubuntu1
  Kandidat: 3.4.1-0ubuntu1
  Versionstabelle:
 *** 3.4.1-0ubuntu1 0
        500 http://at.archive.ubuntu.com/ubuntu/ precise/main amd64 Packages
        100 /var/lib/dpkg/status

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: gnome-screensaver 3.4.1-0ubuntu1
ProcVersionSignature: Ubuntu 3.2.0-24.37-generic 3.2.14
Uname: Linux 3.2.0-24-generic x86_64
ApportVersion: 2.0.1-0ubuntu7
Architecture: amd64
Date: Tue May 22 14:56:24 2012
GnomeSessionIdleInhibited: No
GnomeSessionInhibitors: 1: AppId = rhythmbox, Flags = 4, Reason = Wiedergabe
GsettingsGnomeSession:
 org.gnome.desktop.session idle-delay uint32 300
 org.gnome.desktop.session session-name 'ubuntu'
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120425)
ProcEnviron:
 LANGUAGE=de_AT:de
 PATH=(custom, no user)
 LANG=de_AT.UTF-8
 SHELL=/bin/bash
SourcePackage: gnome-screensaver
Symptom: security
Title: Screen locking issue
UpgradeStatus: No upgrade log present (probably fresh install)
WindowManager: No value set for `/desktop/gnome/session/required_components/windowmanager'