[BUG] Failure to Update Player Inventory

[EpicBirb]

Prerequisites

• [x] I made sure I am running the latest development build
• [x] I tried to look for similar issues before opening a new one
• [x] I have set debugmessages=true in config to diagnose my issue
• [x] I have redacted session tokens and passwords before attaching screenshots

Minecraft Version

1.20.1; 1.20 (using viaproxy to connect to 1.21.5)

Console Client Version

GitHub build 285, built on 2025-05-22 from commit f785f50

Expected Behavior

When opening an external inventory (in this case a chest boat) and being given an item (in this case 256 cod). I should expect that I should be able to view the same given items in my player inventory as well as the external inventory.

Actual Behavior

Upon tinkering with /inventory, it appears that the given items are only present in the external inventory and not the player inventory. Upon closing the external inventory and giving the player an additional 256 cod, the existing cod that was given before will not appear in the player's inventory (viewable with /inventory 0 list)

Steps to Reproduce the bug

1. Boot up a LAN world on 1.20.1
2. Let MCC connect to the LAN world using localhost:<port>
3. Let MCC get into a nearby chest boat (/entity ChestBoat use)
4. Run /entity ChestBoat use repetitively until an inventory is opened
5. Confirm that both inventories (the newly opened one and the player inventory) is empty.
6. On the client that is hosting the world give MCC 256 cod.
7. Run /inventory <id of opened inventory> close
8. Run /inventory 0 list

You should see that the cod that was given to MCC is not present in the player's inventory

Attach screenshot here (If applicable)

Anythings that could help diagnosing the bug

Device

Desktop

Operating System

Windows

Server Address (If applicable)

No response