I have a similar problem in that, after having used the number pad successfully for several years, it suddenly has started to function as a scroll up and down and I have been having to resort to using the numbers above my letter keys. This is slowing me down, especially as I am currently working on spreadsheets for tax returns.
I have had a situation previously where letters were coming up instead of numbers, but fixed that with a reboot. This is new and is not responding to anything that I have tried so far.
Any advice? I am using OS X v 10.9.5