Shift-clicking a shulker box from the hotbar into your inventory can sometimes create a duplicate of it, one in each slot the box was in, being the hotbar slot and the slot you moved it to

What I expected to happen was...:
The box to move, without duplicating itself

What actually happened was...:
The box first appears only once, but it shows as duplicated after you update your inventory by opening another shulker box

Steps to Reproduce:
1. Place a shulker box in creative

2. Fill it with some items, I used each color of glass in the one I found the bug with

3. Break the shulker box, so that it goes into your hotbar

4. Shift click the shulker box into inventory, and then close your inventory

5. When you open another shulker box, 2 copies of the shulker box will be in your inventory, 1 in the hotbar slot you moved it from, and one in the inventory slot you moved it to

I could not reproduce this in survival, but I also couldn't get it to work every time on creative either, further testing might be needed to determine whether or not this affects survival too.