Switching language on lockscreen shows desktop on second monitor

Hardware:
Lenovo IdeaPad Y570
Second monitor connected via HDMI port

Steps to reproduce:
Configure two keyboard languages (I have EN-Dvorak and RU)
Lock the screen
Switch from EN to RU

What happens:
The applications that would be drawn on the laptop's screen are drawn on the screen of the attached monitor.

What should happen:
No information behind the lockscreen should be revealed until the user enters the correct password.

Software:
Ubuntu 12.10
cinnamon:
  Installed: 1.6.7-0ubuntu1~quantal1
primus:
  Installed: 201302241855git~quantal1
bumblebee:
  Installed: 3.1-1~quantalppa1
bbswitch-dkms:
  Installed: 0.5-1~quantalppa1

Relevant configuration:
/etc/environment
PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games"
CLUTTER_PAINT=disable-clipped-redraws:disable-culling
CLUTTER_VBLANK=True

ProblemType: Bug
DistroRelease: Ubuntu 12.10
Package: gnome-screensaver 3.6.0-0ubuntu2.1
ProcVersionSignature: Ubuntu 3.5.0-25.39-generic 3.5.7.4
Uname: Linux 3.5.0-25-generic x86_64
ApportVersion: 2.6.1-0ubuntu10
Architecture: amd64
Date: Fri Mar 1 23:11:20 2013
EcryptfsInUse: Yes
GnomeSessionIdleInhibited: No
GnomeSessionInhibitors: None
GsettingsGnomeSession:
 org.gnome.desktop.session idle-delay uint32 0
 org.gnome.desktop.session session-name 'ubuntu'
InstallationDate: Installed on 2012-10-20 (133 days ago)
InstallationMedia: Ubuntu 12.10 "Quantal Quetzal" - Release amd64 (20121017.5)
MarkForUpload: True
SourcePackage: gnome-screensaver
Symptom: security
Title: Screen locking issue
UpgradeStatus: No upgrade log present (probably fresh install)