Board Thread:Bug Reports/@comment-26141035-20150525204203

You can currently dupe spears (and other throwables less reliably) by simply dropping the item after releasing the charge (or clicking in unchargable throwables). This creates a race condition of sorts that the drop should win while also still allowing the item to be thrown. This will result in the player being able to recover the initial throwable (with no durability damage) as well as the projectile thrown.

This can be corrected by checking that the itemstack is actually in the player inventory at the time the spear is created in the world. 