Wither´s actual health isn´t shown on his health bar if he has {NoAI:1}

What I expected to happen:
The wither´s boss health bar to show the health that Wither truly has

What truly happened:
The wither´s health bar only shown his full health all the time

How to reproduce:
1. Write this command in chat: /summon WitherBoss ~ ~1 ~ {NoAI:1}