When an upward facing dropper connected to another inventory item (dropper, chest, etc.) and is activated by redstone, it will "send" the item to the next inventory, but the item is actually lost.
Edit - What it does is delete all but the last item. I have been able to reproduce this with Ender pearls, signs, and bones.
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[media]
Unable to reproduce. Item arrives safely in the top chest.
Duplicate of MC-7654.