/summon command data tag:Invurnerable

The data tag "Invurnerable" was suppose to make a mob invincible from attacks, potions, fall damage, etc.

What actually happened is that I can still hit the mob and it takes damage and dies easily

How to go to the bug:
1.Get a command block from command "/give <playername> minecraft:command_block"
2.Place the command block and right-click the block
3.Type in /summon Cow ~ ~ ~

4.Select Ok in the the command and put a redstone torch next to the command block
5.Get Diamond Sword and Hit the mob