Using any hotbar item automaticcaly switches to slot 4

i have my hotbar setup with sword slot 1 pickaxe slot 2  etc when i try to use any slot on hotbar it automatically switches to slot 4. Even if i have nothing in that slot i the am using my hand to break a block or swing my sword.  i have been playing for a while now no new updates and suddenly this happened. I have even tried a new world and still this happens.