Sometimes can not unlock screen locker

[Tomas Brandysky]

I have Laptop with connected monitor over DVI cable.
I am using desktop as split between these two monitors (Xinerama)
1) I let the screensaver start
2) I move the mouse and I am asked for the password to unlock the screen
3) There are two independent windows shown to type in the password (one on both of monitors)
4) Sometimes when I type the password on 2nd monitor (external monitor) it is not excepted
5) I need to type the same password to the window displayed on primary monitor (on Laptop)

This doesn't happen all the time. At least it doesn't happen when I lock the screen manually (ctrl+alt+L)

ProblemType: Bug
DistroRelease: Ubuntu 13.04
Package: kscreensaver 4:4.10.2-0ubuntu1
ProcVersionSignature: Ubuntu 3.8.0-19.30-generic 3.8.8
Uname: Linux 3.8.0-19-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.9.2-0ubuntu8
Architecture: amd64
Date: Thu May 2 16:10:39 2013
InstallationDate: Installed on 2011-12-23 (495 days ago)
InstallationMedia: Kubuntu 11.10 "Oneiric Ocelot" - Release amd64 (20111012)
MarkForUpload: True
SourcePackage: kdeartwork
UpgradeStatus: Upgraded to raring on 2013-04-26 (6 days ago)