Menus prevent gnome-screensaver from locking the display

Steps to Reproduce:

Open a menu of a Application, for Example the Firefox extra menu. Wait that the display is switching off. After you activate the monitor again you see the normal screen and not the locking screen. You can do anything what is not closing the open menu. After you have closed the menu the screen will lock.

Expected behavior:

The screen is locked after the monitor has switched off. It should not matter if you have a opened menu!

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: gnome-screensaver 3.4.0-0ubuntu1
ProcVersionSignature: Ubuntu 3.2.0-23.36-generic-pae 3.2.14
Uname: Linux 3.2.0-23-generic-pae i686
NonfreeKernelModules: nvidia
ApportVersion: 2.0.1-0ubuntu1
Architecture: i386
Date: Wed Apr 11 20:24:08 2012
EcryptfsInUse: Yes
GnomeSessionIdleInhibited: No
GnomeSessionInhibitors: 1: AppId = rhythmbox, Flags = 4, Reason = Wiedergabe
GsettingsGnomeSession:
 org.gnome.desktop.session idle-delay uint32 60
 org.gnome.desktop.session session-name 'ubuntu'
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Beta i386 (20120328)
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: gnome-screensaver
UpgradeStatus: No upgrade log present (probably fresh install)
WindowManager: No value set for `/desktop/gnome/session/required_components/windowmanager'
XorgConf:
 Section "Device"
  Identifier "Default Device"
  Option "NoLogo" "True"
 EndSection