cant unlock sporadically it grays out the input field

[u-foka]

Sporadically after the screen is locked when I try to unlock it the input field looks gray and ignores any input.
It happened on saucy and now also on trusty..

Tryed to hit ESC to hide and redisplay the prompt, or event suspending and waking the computer but none helps except going to a tty logging in and killing the screensaver.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: gnome-screensaver 3.6.1-0ubuntu9
ProcVersionSignature: Ubuntu 3.13.0-8.28-generic 3.13.2
Uname: Linux 3.13.0-8-generic x86_64
ApportVersion: 2.13.2-0ubuntu4
Architecture: amd64
CurrentDesktop: Unity
Date: Sun Feb 16 14:04:09 2014
GnomeSessionIdleInhibited: No
GnomeSessionInhibitors: None
GsettingsGnomeSession:
 org.gnome.desktop.session session-name 'ubuntu'
 org.gnome.desktop.session idle-delay uint32 300
InstallationDate: Installed on 2014-02-14 (1 days ago)
InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Alpha amd64 (20140211)
SourcePackage: gnome-screensaver
UpgradeStatus: No upgrade log present (probably fresh install)