Hotbar glitch.

When you have more then 1 stack of items in your inventory, and you click another item into on of them, creative or survival, there will be more then 1 of them. For ex. if u have 2 stacks of diamonds, and you click 1 piece of diamond armor, there will be 2 in your hotbar, you wont have 2, but there will be 2 in your hotbar.