Updated description by GoldenHelmet
- Craft or /give @s 2 shulker boxes of the same color.
- Place both shulker boxes.
- Mine one of the shulker boxes and put it in your inventory, but not in your hotbar.
- Try to pickblock the other shulker box.
The matching shulker box in your inventory moves to your hotbar.
The matching shulker box in your inventory does not move to your hotbar.
The expected result does occur if you have never placed and mined the shulker box in your inventory. If you switch to creative and pickblock the placed shulker box, it will put a new one in your inventory rather than bringing down the mined one.
After a shulker box has been created and can be quick selected with pick block. However after it has been placed and picked back up, pick block will no longer work with that shulker box.