I can confirm this bug, though for me using the keyboard does prevent the screen from fading no matter which screen I'm on. I actually came upon this bug by accident, as I had mainly only used my second screen for games (keypad doesn't prevent the screensaver anyway) and MPlayer (which disable the screensaver). To deal with my screensaver problems I tried a simple script to disable the screensaver upon opening the selected program and re-enabling it once opened.
What I found through that is that when I returned to my main display, if I was only moving my mouse it wouldn't prevent the screensaver, while moving it to the secondary display did. To summarize, I found that it wasn't only activity on :0.0 that was preventing the screensaver from activating, but from whichever display ran gnome-screensaver (which by default is generally :0.0). To confirm, try this:
Run:
gnome-screensaver-command --exit
(To terminate the default session) and then on any secondary display run:
gnome-screensaver
And the bug should be on opposite screens as it was before.
I can confirm this bug, though for me using the keyboard does prevent the screen from fading no matter which screen I'm on. I actually came upon this bug by accident, as I had mainly only used my second screen for games (keypad doesn't prevent the screensaver anyway) and MPlayer (which disable the screensaver). To deal with my screensaver problems I tried a simple script to disable the screensaver upon opening the selected program and re-enabling it once opened.
What I found through that is that when I returned to my main display, if I was only moving my mouse it wouldn't prevent the screensaver, while moving it to the secondary display did. To summarize, I found that it wasn't only activity on :0.0 that was preventing the screensaver from activating, but from whichever display ran gnome-screensaver (which by default is generally :0.0). To confirm, try this:
Run:
gnome-screensav er-command --exit
(To terminate the default session) and then on any secondary display run:
gnome-screensaver
And the bug should be on opposite screens as it was before.