Holding delete key activates the Shut Down computer dialog box.

When I press and hold the delete key for a few seconds on my Aluminum Macbook (late 2008) running Lion (and previously Snow Leopard) the Shut Down computer dialog box appears (about 90% of the time.) This behaviour is not attached to any specific program. It's really annoying when I'm just trying to backspace. I've tried closing all running services. I've checked keyboard shortcuts. Any explanation for this? Anyone have a fix for this behavior?

Thank you.