Please describe the problem:
If you copy and past (e.g. a password) and then lock your screen and go away someone else can walk to your computer can click 'Leave Message' and press Ctrl+V in order to reveal the password (or whatever content) you had in your clipboard before you locked the screen.

Steps to reproduce:
1. copy and paste some sensitive information
2. Lock your screen
3. 'Leave Message' and press Ctrl+V to see the formerly copied password


Actual results:
gnome-screensaver helps attackers to revela your copied passwords (or other possibly sensitive information)

Expected results:
Since there is this "leave a message" feature I would expect the screensave to clear the clipboard before activation.

Does this happen every time?
Yes

Other information:
no further information available, i hope it's clear what i talk about.