Dell KM714 Keyboard - I've read various posts about folks not knowing how to toggle Numlock on this keyboard.  

What I've found is that sometimes I go to enter numbers and the number pad acts as arrows or something.

Somehow either the left shift key and/or the left control key play a role here.  I'll discover the numbers not working (Not sure what turns them off).  Sometimes I have to tap the left shift key, sometimes it's the left control key - then I get the number pad functionality back.

I've followed the tips in other threads to turn off "Use keyboard as mouse".  There's no software for this keyboard other than the Receiver control panel to pair devices.  

So - what causes the Numlock to disengage (seemingly randomly)?  And what software allows for the configuration of the keyboard functionality?  

I've tried two of these keyboards thinking it was a hardware defect.

Thanks.