Hopper, Dropper, Dispenser UI

My hotbar is full of junk so I switch out the slot so its empty; but when you enter either the hopper, dropper, or dispenser's UI and exit it pulls out the items from your inventory and puts them into your hotbar.

Steps to reproduce:
1. Have your all of your hotbar slots full of any item
(Make sure all or most of your hotbar slots are full)
2. Take out the items in your hotbar so that you have vacant slots
3. Access either the hopper, dropper, or dispenser's UI