screen lock does not disappear even after sending interrupts

[Tapas Mishra]

I am using Ubuntu 10.04 64 bit with all the updates.
The problem I am reporting is with gnome lock.
Which should lock the screen only after a certain period of time the
computer has been inert.
What is happening in this process is when I see the screen with my
browser and other active windows open
slowly after some time this becomes dark and lock.
The time which is set is in
System --->Preferences-->Screen Saver
is 60 minutes.
The problem I am reporting is when at the end of 59th minutes say  55
seconds or so I see that a screen saver is slowly becoming active then
I
do some activity with my keyboard or use my mouse so that the screen
saver does not become active these events do not have any effect on
this process and I get a
screen locked.
Ideally on an event like pressing a key or moving mouse pointer to
some random location irrespective of 59th minute and last few seconds
when I see the screen lock slowly coming
the computer was not idle so screen saver should not become idle.

-- 
Tapas