Custom LOOM result cannot be taken without pattern item

[Kakkuh]

Expected behavior

The custom LOOM inventory should allow the player to take the result banner when using:
banner + dye
banner + dye + pattern

Exactly the same as a real loom block.

Observed/Actual behavior

When opening a custom loom inventory using InventoryType.LOOM, the result item cannot be taken unless a banner pattern item is used.

If the player uses banner + dye, the result appears visually, but it cannot be picked up.

If the player adds a banner pattern item, the result becomes available.

This does not happen with a real loom block.

Steps/models to reproduce

1. Open a custom loom:

Inventory inv = Bukkit.createInventory(player, InventoryType.LOOM);
player.openInventory(inv);
or any other method to open an InventoryType.LOOM inventory

2. Put a banner into slot 0
3. Put a dye into slot 1
4. Select any banner design using the UI
5. Try to take the result -> it cannot be taken
6. Now put a banner pattern item into slot 2 and try again, now it works.

Plugin and Datapack List

Only the testing plugin

Paper version

This server is running Paper version 1.21.10-115-main@af06383 (2025-11-21T23:42:01Z) (Implementing API version 1.21.10-R0.1-SNAPSHOT)
You are running the latest version
Previous version: 1.21.8-60-29c8822 (MC: 1.21.8)

Other

No response

[Lulu13022002]

Those inventories are not proper menu i would recommend using the MenuType API if you can or wait for the linked issue to be fixed.