We don't know if this is intended or not, but I figured that I would report it anyway in case it is not: boomerangs stay in their slot in the inventory when thrown, unlike spears and vanilla tridents.

I think its intended because it takes durability as soon as it hits something. If not it might be there to stop someone from not being able to pick up the boomerang because their inventory became full after they threw it and it would disappear thus deleting the boomerang.