When you apply the Invisible tag to an Armor Stand, it will also be invulnerable.

What I expected to happen was...:
The armor stand is invisible, and is not invulnerable.

What actually happened was...:
The armor stand is invisible, but it is invulnerable.

Steps to Reproduce:
1. Type this command: /summon ArmorStand ~ ~ ~

2. You spawned an invisible armor stand. You can see its name. The armor stand itself is right under the name.
3. Try to punch the armor stand. The armor stand wont go away. You can see the armor stand in spectator mode (/gamemode 3)
Also, if you want to remove the armor stand, you can type in this command, while standing next to the armor stand: (/kill @e[type=ArmorStand,r=3])