1. Full screen an application, say, for example, a presentation in a web browser
2. Suspend
3. Resume
You'll see a screen with whatever was on the screen when you suspended, but you won't see the screensaver unlock dialog. Try to type or use the mouse and you'll get what appears to be no response. However, if you type your password and hit enter then suddenly everything becomes responsive again.
Alternatively, switch to a terminal and kill the full-screen app. Then the screensaver unlock dialog is visible.
Marked as a security vulnerability, because it means the contents of my screen from before suspend is revealed on resume.
I have just reproduced the bug again. First time, I saw it was last night when I was about to give a presentation. I ended up having to give the presentation from memory without slides, which was uncomfortable for everyone.
ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: gnome-screensaver 3.2.0-0ubuntu1
ProcVersionSignature: Ubuntu 3.0.0-12.20-generic 3.0.4
Uname: Linux 3.0.0-12-generic x86_64
ApportVersion: 1.23-0ubuntu3
Architecture: amd64
Date: Thu Nov 3 08:59:51 2011
EcryptfsInUse: Yes
SourcePackage: gnome-screensaver
UpgradeStatus: Upgraded to oneiric on 2011-07-26 (100 days ago)
I just tried this on current precise with a full screen firefox and an external display, and it works fine. On resuming I see the screen saver unlock dialog, type my password, and I'm back to firefox.
Can somebody else confirm this?