Please describe the problem:
I often attach my notebook computer to a large 1900x1600 LCD monitor, then close the lid on the computer. The screensaver does not appear on the external monitor when the lid is closed, but it does when the lid is open.

In my case I have an NVidia graphics card and am using the proprietary nvidia driver. Note that I am typically not running in dual monitor mode; the external one is the primary monitor and the laptop's attached display is disabled.
GNOME Power Manager is set to "Do nothing" when the laptop lid is closed, which is indeed the case; if I close the lid, the external display generally stays functional (which is different from if I had set it to "Blank screen").

Steps to reproduce:
1. Attach notebook computer to external monitor and configure video to display on it.
2. Launch the screensaver (eg: for example, lock the screen).
3. Close the lid on notebook computer.
4. Open the lid on notebook computer.

Actual results:
When computer's lid is open, the screensaver appears properly on all attached screens. When lid is closed, the screensaver disappears on all attached screens even though the external one is still meant to be visible and the laptop's own screen is not actually in use.

Expected results:
*Duh* :P

Does this happen every time?
Yes. This even happens while the screensaver is running!

Other information: