The Arcane Tablet can learn items that have no EMC value if you use the crafting table in the inventory to manually craft something that has no EMC value. I found this in Sky Odyssey when manually crafting the Mystical Agri. Infusion Stone in the tablets crafting grid. You cannot pull the items out of the tablet, but it does show the item with a quantity of "Infinite" . So this is NOT a dupe bug, but a most likely unintended interaction.