Whenever you use the /summon command with the entity "Item" (using the data tag {Item:{id:###}}), the item that is summoned cannot be picked up. It moves out of the way when you place blocks on it and it burns in lava but you can't pick it up. Also, when it falls into a hopper (it will bounce off if the hopper is powered like a regular item would), the item disappears and is Not in the hopper or anything the hopper is attached to.