What I expected to happen was that the banned item wouldn't spawn e.g. Invisibility Potion. Unluckily it works and people can get access to the banned item.

What actually happened was the player turned invisible and we couldn't do much about it.

1. Place a block with a button it, and equip the potion/egg.
2. Shift while in front of the button.
3. This is were the bug comes into play. As you shift and right click, it fully allows you to spawn/drink the item held in hand.

Thank you for your time.