❗ Checklist

• I am using the official english version of Slimefun and did not modify the jar.
• I downloaded the official version from the new build site Blob Builds.
• I am using an up to date "DEV" (not "RC") version of Slimefun.
• I am aware that issues related to Slimefun addons need to be reported on their bug trackers and not here.
• I searched for similar open issues and could not find an existing bug report on this.

📍 Description

Forward from SlimefunGuguProject/Slimefun#1058 and confirmed in the official version.

When copying a slime head in the inventory and placing it back into the inventory, there is a chance the item may disappear.

📑 Reproduction Steps

This issue affects all Slimefun heads. Using synthetic sapphire as an example:

Place a synthetic sapphire (PLAYER_WALL_HEAD) attached to the side of a block and aim the crosshair at it.
Open the inventory and middle-click to copy the synthetic sapphire in the inventory.
Observed Behaviors:

Case 1:

Original synthetic sapphire is in the non-hotbar slots.
Place the copied item into the non-hotbar slots.
Result: No issue occurs.
Case 2:

Original synthetic sapphire is in the hotbar.
Place the copied item into the non-hotbar slots.
Result: No issue occurs.
Case 3:

Original synthetic sapphire is in the non-hotbar slots.
Place the copied item into the hotbar.
If the hotbar already contains at least one synthetic sapphire, the item disappears.
If the hotbar contains no synthetic sapphire, the item quantity becomes 1.
Case 4:

Original synthetic sapphire is in the hotbar.
Place the copied item into the hotbar.
Result: The item disappears.

💡 Expected Behavior

No item disappears.

📷 Screenshots / Videos

No response

📜 Server Log

No response

📂 /error-reports/ folder

No response

💻 Server Software

Paper

🎮 Minecraft Version

1.20.x

⭐ Slimefun version

Slimefun vDev-1160

🧭 Other plugins

No response

This issue may affect all Slimefun items, not just head-type items.

Caused by MiddleClickListener