I have the Linux version of the student edition of Mathematica 4.1. I've been having this problem ever since I installed it, although I only recently realized the connection as it just seemed random to me before.
Basically when I have numlock on, strange things happen (this is all dealing with the graphical front end). When I try to use special functions like matrices and so forth, I cannot select the proper input boxes at all. Even worse, backspace doesn't work. If I hit backspace, instead of deleting the previous character some kind of character that can't be properly displayed appears (it's just a lightly shaded square).
That's strange, but what is really strange is that the mouse seems to be affected as well. I can't properly highlight what I have typed with the mouse and links in the documention don't seem to work (I click on them, but nothing happens).
Now, I turn off numlock and all these problems, even the mouse issues, go away. I don't even have to restart Mathematica. It's like a switch. When numlock is on I get this strange behavior, but when it's off everything works fine. Naturally I just turn off numlock when I use Mathematica now (Although it actually took me a while to notice the connection as it's just something I would never have even thought of.), however it would be nice if I could figure out what would cause such strange behavior (besides which, I like to use the numpad to enter numbers). Linux has been my primary operating system for a number of years now and I've never had this kind of problem with any other program. It's definitely a mathematica specific issue.
Thanks for any help you can offer.