I have some follow up on this, sorry if it's too long.
Using the "in keyboard" numpad, all RCS and control surface commands work, its just the 1/4 and 3/6 combinations that don't. When hit simultaneously there is no control surface motion or RCS fire. When hit sequentially, the first command takes precedence and the later is inactive. Also the cross-controlled key command1/6 and 3/4 work. The keyboard otherwise functions normally.
I have a Dell M1710 2.00 GHz Centrino processor. 4GB RAM (3.25 useable) 512MB video running WinXP Pro. The same issue occurs on my Dell Inspiron laptop but not on my Dell Dimension desktop. I haven't edited the keymapping files from their default and can duplicate the problem in all 7 of my Orbiter installations across several vessels. The RCS effect is less noticeable in spaceflight than the control surface issue is in atmospheric flight. The ships are still flyable.
I purchased a USB numpad and the problem disappeared. It may be that while the "in keyboard" numpad can function, it's function is limited or distorted. Look at your control surface and RCS action with your key commands. I'd be curious to see if this is a common laptop issue or just clustered in certain brands.
Thanks,
Ben