Wither´s custom name doesn´t show up above his health bar

What I expected to happen was...:
That the custom name would show above the wither´s boss health bar

What actually happened was...:
The name above the health bar was just basic "Wither"

Steps to Reproduce:
1. write to chat : "/summon WitherBoss ~ ~1 ~ {CustomName:"Vladko",NoAI:1}"