Beacon item duplication glitch

Not sure if this has been reported already. I searched and couldn’t find anything.

How to reproduce

1. Use the Pocket UI profile.
2. Place a beacon in survival mode.
3. Have a stackable item in your inventory.
4. Open the beacon UI.
5. Double press the item, and the stack will double in size.

Note that this only works for some item slots. If it doesn’t work, try moving the item to another slot, and repeat step 5.