Hopper Item Duplication When Items Thrown In

When you throw items into a hopper it duplicates/makes multiples of the item.

What I expected to happen was...:
Only the specified amount you dropped should be visible in the hopper gui

What actually happened was...:
The item was duplicated/multiplied

Steps to Reproduce:
1. Place a Hopper
2. Have something to throw i.e. glass
3. Throw your chosen item(s) into the hopper
4. Look in the hopper to find duplicated/multiplied items.