items in hand doesn't change properly when "Item Switching Animation" is on

[SystemlessDev]

How to reproduce:

• Make sure that "Item Switching Animation" is on
• Run /give @a skull 1 3 {SkullOwner:Sk1er} and /give @a skull 1 3 {SkullOwner:Systemless_} to get two heads
• Hold one of them, open the inventory and switch the slots around
• See that the head in your hand doesn't change

hand.switching.mp4