Hoppers don't search for items they need

Hoppers that have a partial stack of an item in their inventory do not detect if the chest above them has another stack of that item unless it is in the first occupied slot.

What I expect to happen: If a hopper has five incomplete stacks (or up to four complete stacks and one or more incomplete ones) in its inventory, it would search for items of the same types as are currently in its inventory in the container above, and if any are present pull them into the hopper regardless of their slot in the container.

What actually happens: Hoppers only pull from the first occupied inventory slot of chests above them, even if an item in a different slot could complete a stack in its own inventory.

Steps to reproduce:
1. Place a chest
2. Place a hopper below the chest
3. Place five stackable items in the hopper
4. Place an item that is not in the Hopper in the first inventory slot of the chest, followed by items that are in the hopper.