Last week, all of a sudden, the numpad of my laptop stopped working. Well, it didn't really stop; numbers weren't working at all, that's right, but the "+" sign was highlighting text, and I could still use the small "Enter" and "Page up/down" keys without problems.
Apparently it happened without a reason, but I was definitely sure it was going to be quite easy to fix the problem. Until I realized that none of the solutions I found on the Net (Like this one and this one) was working for me.
A lot of forum threads suggested to check whether the problem gets solved by pressing key combinations like <CTRL><SHIFT><NUMLOCK> or <CTRL><ALT><NUMLOCK>, or something like that. None of these solutions worked for me; however in this article (which is one of those that mainly suggest the key combination) there's something written that has something to do with the solution: it's about the "Mouse keys".
After a long day feeling dumb as hell, I finally noticed that one of the switches in the Gnome3 Universal Access area was set to "on" (while I normally have all of them set otherwise). Damn, it was the Mouse Keys stuff. Meaning: I actually allowed the pointer to mess around.