Creative item copy results existing item being client-side only

Description

When trying to do Minecraft's item copy in creative mode (using mouse wheel click), and when there is no slots remaining in hotbar, the pre-existing item goes into the player's inventory. However, when the inventory is not being watched, the item in the inventory remains to be the client side, and when player changes the gamemode (survival / adventure) or use the inventory command like `/clear`, the item becomes completely client side. (Before those actions, in creative mode, simply just watching the inventory makes it server-side)

Steps to Reproduce

1. Fill hotbar with any item

2. Wheel click (copy item, doesn't matter whether it is a ctrl (nbt) click or not) any item which is not in hotbar in Step #1

3. Change your gamemode or use `/clear` and see the inventory.

Expected Behavior

The items in inventory must be server-side, and should be able to interact with it.

`/clear` should clear the inventory, including the items in inventory.

Observed Behavior

The item becomes client-side and not a single interaction successfully works

`/clear` doesn't remove those items.