I can confirm this is still an issue as of 25w20a, and am able to consistently reproduce the issue with the following steps:
Open your inventory in creative mode
Go to any creative mode items tab
Hold down SHIFT (and don’t let go for the remainder of these steps)
Pick up an item (or a stack of items) with left-click
Place the item stack in any slot of your hotbar with left-click
Left-click on the updated item stack in your hotbar
As expected, the item is removed from your inventory. However, it appears that, under this circumstance, the client fails to send the set_creative_mode_slot packet to the server, causing the desync. This also happens in singleplayer.
Benj_2005
I can confirm this is still an issue as of 25w20a, and am able to consistently reproduce the issue with the following steps:
Open your inventory in creative mode
Go to any creative mode items tab
Hold down SHIFT (and don’t let go for the remainder of these steps)
Pick up an item (or a stack of items) with left-click
Place the item stack in any slot of your hotbar with left-click
Left-click on the updated item stack in your hotbar
As expected, the item is removed from your inventory. However, it appears that, under this circumstance, the client fails to send the
set_creative_mode_slotpacket to the server, causing the desync. This also happens in singleplayer.