For some reason in creative and survival the number 1 slot keeps changing and giving you a different block or item. I am not able to use my sword in that spot to battle monsters. I have to place it in another spot. In creative it will switch to Grass or a block that I did not opt in.

I tried using it with and without any mods and even went to default and it is repeating itself. This effects all modes in the game and this is within minecraft itself.