screen saver refuses to unlock given correct password

[Alon Ziv]

Since upgrading to Ubuntu 12.04, I am unable to unlock my computer after it enters the screensaver.
Log-in does work (graphical or text-VT); /var/log/auth.log just includes lines like

May 15 20:46:39 dragon gnome-screensaver-dialog: pam_unix(gnome-screensaver:auth): authentication failure; logname= uid=1000 euid=1000 tty=:0.0 ruser= rhost= user=alon

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: gnome-screensaver 3.4.1-0ubuntu1
ProcVersionSignature: Ubuntu 3.2.0-24.37-generic 3.2.14
Uname: Linux 3.2.0-24-generic x86_64
NonfreeKernelModules: fglrx
ApportVersion: 2.0.1-0ubuntu7
Architecture: amd64
Date: Tue May 15 20:51:11 2012
GnomeSessionIdleInhibited: No
GnomeSessionInhibitors: None
GsettingsGnomeSession:
 org.gnome.desktop.session idle-delay uint32 600
 org.gnome.desktop.session session-name 'ubuntu'
InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Release amd64 (20111012)
ProcEnviron:
 PATH=(custom, user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: gnome-screensaver
UpgradeStatus: Upgraded to precise on 2012-05-14 (1 days ago)
WindowManager: No value set for `/desktop/gnome/session/required_components/windowmanager'

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.