I can’t remember after which update (of Gnome/Ubuntu) this happened, but each time when I fire up the Gnome Calculator and start hitting the numbers on my keyboard’s keypad, nothing appears in the calculator’s display! Aha, of course, NUMLOCK turned off. So I hit the NUMLOCK key and start banging on the keypad again. Still no numbers appear, but… What the heck, the mouse is moving?
After consulting the all-knowing Google, I found the cause of this rather interesting behavior. Open System → Preferences → Keyboard. Then go to the Mouse Keys tab. Now here’s the million dollar question. Why would somebody ever want to move its mouse pointer with the keypad? Maybe because you broke your mouse slamming it on your desk because you we’re so irritated that you couldn’t use your keypad? I don’t know. I’ve never had the urge to control my mouse pointer using the keyboard. Maybe they’d called it keypad-pointer if it was meant to be controlled by the keypad.
Well, they didn’t, so press Shift + NUMLOCK. This will uncheck the “Pointer can be controlled using the keypad” checkbox. Why was this box checked in the first place? Maybe its the default. Or maybe I once accidentally held down the shift key when I pressed NUMLOCK.
That must be it.