If I inadvertently leave my computer with the cursor at the very edge of the screen, my screen saver fails to engage.

The only way I can get it to activate is to go to the screen saver controls, change the time (from one minute to 2), click apply, and then change it back to the original time. It works fine until the next time the cursor is at the edge.

Is there a way to stop this from happening, that is, to keep the screen saver active no matter where the cursor is?

(Win7 Ultimate 64, AMD Athlon 2core)