privacy and gnome screen lock issue

[Ralph Pichie]

When I return to my laptop and the screen saver has activated
automatically while i was away, I am often able to stop the screen
saver (Cosmos, I believe) and see what was on the active desktop,
including mail and the like, even refresh a Twitter feed. The login
dialog appears, IIRC, when I try to switch desktops or active
applications or launch applications. This just isn't good enough. How
do I get it to immediately lock the screen and refuse all activity
without login?

What is the reason for this? Is it simply a time lag or difference in
triggers between the screen saver and the login function? Perhaps it
varies with the input device that triggers the events? Has anyone else
noticed the same thing?

Manually locking the screen seems to work better, but I have not
tested that after a lengthy period with the screen saver activated.

Version: Ubuntu 11.04 with classic desktop, no effects, running on an
HP 620 laptop.