My Ubuntu 10.04 install was behaving weirdly when I used the numeric keypad. The keys would never generate numbers; rather, they would move the mouse cursor.
Luckily, I found this post:
In short, the solution to turning off this feature is to go into System->Preferences->Assistive Technologies, press “Keyboard Accessibility”, then under “Mouse Keys” uncheck “Pointer can be controlled using the keypad.”
My KVM switch often leaves the shift state down – and the keyboard shortcut for this is Shift + NumLock.