The bug
In Creative mode, the hotbar sometimes becomes desynced if an item is moved immediately before and after switching to the inventory's Survival tab.
To reproduce
Note: Steps 1-4 must be performed in quick succession.
Open the Creative inventory (but not the Survival tab)
Place an item into your hotbar
Switch to the inventory's Survival tab
Move the item to a different slot
Exit and rejoin the world
→ ❌ You now have two of the item
Related issues
relates to
Attachments
Comments

[media]

Cannot reproduce

Can confirm in 1.21.4.