A couple of days ago, when I came back to my computer after a couple of hours, the following window was on my desktop:
The title bar said "gnome-screensaver-dialog". That's it. I just clicked OK, and went on. This has happened to me once before, but a long time ago.
Please note, I just have the plain blank screen as the screen saver.
When you go away from the computer it lock. On the unlock password screen there is a button so that someone can leave a message. Is this a case of somehow a blank message got left?
this is exactly the intended behavior. It is there just in case someone needed you (or your computer) "while you were out". This way, they can leave you a message, without breaching into your computer for that. Say you went to the restroom, and a co-worker wanted to have you look-up something for them, this way, they can just leave you a message and let you know without having to track you down or leave it on a post-it (which may not be available). The only problem here is maybe we should have the devs add a title bar or other such information to the message that will let the user know it is a "while you were out" message, as opposed to just "something from gnome-screensaver".