Unstackable items stack using the /give command

Making my adventure map and using /give command in command blocks and was expecting 3 mushroom stew to take up 3 inventory slots

But instead the 3 mushroom stew stacked in 1 inventory slot, also tested with a diamond sword and the same result.

Steps to Reproduce:
1. /give @p minecraft:mushroom_stew 3
2. You will see they get stacked even thought they are not a stackable item
.