Duplication and deletion of hotbar items in Creative using number keys

While in your inventory, with items in your hotbar, quickly hitting the numbers while in creative mode can cause some items to overwrite others, and create a duplicate of one item, while removing the other. This does not work in survival.

Spam-clicking items causes same effect. Can sometimes disappear even in survival, see MC-4108.

Easy way to reproduce:

• Open the inventory
• Put two different items in slots 1 and 2
• Hold the mouse over slot 2
• Press and hold "1"
• The items will swap a while and eventually the item of slot 1 overwrites the item of slot 2