Can't unassign NumPad+1 command (still being executed when unassigned)

I want to assign the musical notes from A to G to the numpad. By standard, the numbers on the numpad are assigned to note lengths, for example when you press NumPad+1, you will change the currently selected note to a 64th note.
But that's no problem, I'm thinking. I'm just gonna unassign those so I can use them for something else.
The issue is, even after unassigning and assigning other commands to the buttons, the "64th note" command is still being executed when I press 1 on the numpad. It's not assigned to that anymore, yet it's still stuck to doing it. (all the other buttons aren't doing that bug, just this NumPad+1)
Why does this happen? Is it a bug?