Item Duplication Via Hoppers and world loading

When going from the overworld to the nether (and from the nether to the overworld).
Two hoppers facing each other with an item in one moving between them.
When world reloads after moving through a portal the item in the hopper is duplicated.

Only a very small chance of happening as the item (I assume) must be moving between the hoppers (and not in any single one) just as the world is unloaded. Tested and happens in the overworld and nether just by walking through a nether portal (multiple times to reproduce).