Summary:
When opening the inventory, empty slots are visible. If you try to "take" an item from this slot, they will disappear. These slots end an incomplete row of items.
Works in both pocket and classic interfaces.

If you try to "take" an item from an empty slot and close the inventory, the player will can no longer interact with the world. The placement of the blocks will be "phantom" and the attempt to open the inventory will fail.

Steps to reproduce:

1. Go to inventory on any tab with items.
2. Try to "take" an item from an empty slot (by simply clicking on an empty slot).
3. Close inventory.
4. Try to open your inventory, place block / break.
5. Reload the world.

Observed results:
There are empty slots in the inventory.
After trying to "take" an item from an empty slot: inventory won't open, blocks will not actually be placed.

Expected results:
There should be no empty slots in your inventory.
The player should not stuck in the world.

Image: