When I drop an item onto an empty hopper, and I notice it didn't get 'sucked in', I expect the hopper to remain empty.
Instead it puts the item into it's inventory without actually sucking up the item.
How To reproduce:
Put down a container. This may be a hopper, a chest or a dispenser. Put down hopper A, pointing into the container (by SHIFT-clicking the container). Put down hopper B, pointing into hopper A. Throw items onto hopper B until one remains sitting on it's surface. Notice how the item shows up in hopper B's inventory, goes through hopper A's inventory, and stacks up in the final container.