InventoryClickEvent does not always fire when placing an item into slot 0 or 1 of a villager merchant inventory. It almost always fires, but occasionally will simply not run my code on clicking an item into the slot.

I am cancelling the event on every click. Have tested by spam-clicking, and by waiting 2 seconds between each click. The event not firing does not seem to be consistent, as it can take anywhere between 0 and several hundred successfully canceled clicks before the item is placed into the slot. The trade can then be completed successfully (which I am trying to prevent).