screensaver shows old screen content on return from sleep

when gnome-screensaver activates after an idle period, and so then the screen blanks, then pushing the shift key to wake the monitors and to request that gnome-screensaver display an authentication box sometimes causes the old screen (pre-lock) to display briefly before the screen redraws blank with an authentication box. One can't interact with the old display, and it's brief, no more than a second before repaint, but from a privacy standpoint it's disturbing that the content is briefly visible.

I have gnome-screensaver configured to blank the screen on idle rather than to display pictures or animations.

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: gnome-screensaver 3.2.0-0ubuntu1
ProcVersionSignature: Ubuntu 3.0.0-16.29-generic 3.0.20
Uname: Linux 3.0.0-16-generic x86_64
ApportVersion: 1.23-0ubuntu4
Architecture: amd64
Date: Thu Mar 15 12:38:18 2012
EcryptfsInUse: Yes
InstallationMedia: Ubuntu 10.04 LTS "Lucid Lynx" - Release amd64 (20100429)
ProcEnviron:
 PATH=(custom, user)
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
SourcePackage: gnome-screensaver
UpgradeStatus: Upgraded to oneiric on 2012-01-09 (66 days ago)