Botania 344, Minecraft 1.11.

If a player has two mana tablets in their inventory, the dispersive spark will only fill the first one it finds. The particle effect will still display, even though no mana is being transferred.

My guess: this loop doesn't seem to handle the edge case of the first discovered IManaItem being full. The particle effect still plays because it's helpfully dispensing packets worth 0 mana to my tablet