Item models don't change after reducing the amount in a stack

When a stack of items/blocks is thrown on a hopper and there are still some items left in the stack, it will still show a full stack of items.

Steps to Reproduce:

1. Place a hopper
2. Fill the hopper with 4 unstackable items and 1 stackable item
3. Throw a full stack of the same stackable item onto the hopper

Observed Results:
The 3D item model doesn't represent a model of just 1 item

Expected Results:
The 3D item model should represent a model of just 1 item.