right screen occasionally shown in dual-screen mode

[Till Halbach]

Has happened to me 4 times so far, but haven't been able to nail it down. Am attaching a photo as proof.

ProblemType: Bug
DistroRelease: Ubuntu 13.10
Package: gnome-screensaver 3.6.1-0ubuntu7
ProcVersionSignature: Ubuntu 3.11.0-18.32-generic 3.11.10.4
Uname: Linux 3.11.0-18-generic x86_64
ApportVersion: 2.12.5-0ubuntu2.2
Architecture: amd64
Date: Tue Apr 8 09:34:14 2014
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 2013-11-21 (137 days ago)
InstallationMedia: Ubuntu 13.10 "Saucy Salamander" - Release amd64 (20131016.1)
MarkForUpload: True
SourcePackage: gnome-screensaver
UpgradeStatus: No upgrade log present (probably fresh install)