Leaving Unity in "switcher" (Super+S) will not lock screen

When I leave Unity in "switcher" mode (all 4 workspaces visible, Super+S) and leave my computer for a while, returning to it will show the Desktops. Only when I select a Desktop from the switcher will it show the lock screen.

Preconditions:

 * System Settings -> Brightness and Lock -> Turn screen off when inactive for: 1 minute, Lock: on, Lock screen after: Screen turns off

How to reproduce:

 1. Have any application open on workspace 1
 2. Enable the switcher (Super+S) or click on "Workspace Switcher" in Unity
 3. Wait for 1 minute for the screen to turn off
 4. Move the mouse

Expected outcome:

 * The password entry for the lock screen is displayed

Actual outcome:

 * I can see the workspace switcher and all windows and their live contents
 * Only after selecting a workspace (e.g. by double-clicking) will the lock screen kick in

Reproducability:

 * always

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: unity 5.4.0-0ubuntu2
ProcVersionSignature: Ubuntu 3.2.0-17.26-generic 3.2.6
Uname: Linux 3.2.0-17-generic x86_64
ApportVersion: 1.93-0ubuntu2
Architecture: amd64
CompizPlugins: [core,bailer,detection,composite,opengl,decor,compiztoolbox,place,snap,move,imgpng,grid,vpswitch,resize,regex,session,mousepoll,animation,wall,gnomecompat,fade,workarounds,scale,expo,ezoom,unityshell]
Date: Fri Feb 24 18:49:04 2012
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Alpha amd64 (20120201.1)
ProcEnviron:
 TERM=xterm
 PATH=(custom, user)
 LANG=en_US.UTF-8
 SHELL=/bin/zsh
SourcePackage: unity
UpgradeStatus: Upgraded to precise on 2012-02-24 (0 days ago)