The hotkey for slot 4 doesn't work when sprint jumping

Whenever I am sprint jumping, and I press the "4" key on my keyboard, it doesn't work. All other keys work, and the 4 key does still work when I am standing still, walking, sprinting, or jumping. I have mentioned it to some of my friends and they have said that it happens to them too. You can still scroll to the 4 slot, the hotkey just doesn't work.