When you get a Wither with the NoAI NBT set to 1 and get it under half health, the Wither will get armor on it.
What I expected to happen was...:
The AI-less Wither should not have armor when it's under half health.
What actually happened was...:
Instead, the AI-less Wither actually will get armor when it's under half health.
Steps to Reproduce:
1. Summon a Wither using /summon WitherBoss ~ ~ ~
{NoAI:1}.
2. Get it under half health to see its armor appear.
The NoAI tag doesn't really get rid of all the entity's AI, the only thing it does is it makes them not able to move, fall or attack. Animations are supposed to show even when NoAI is on 1.