Control Keys from hotbar not changing.

I used to have the number 2 key to place an item from my inventory to my hotbar number 5 slot. Now I can't seem to be able to change the numbers, or I can change the numbers but they don't do anything, I have to reset if I want to at least have them work on the default mode wich is key number 2 to slot number 2 ando so on. But if I change to a letter it works. But that's not what I really want. And it makes no sense to be able to change to a letter and not a number.