Withers are affected by the universalAnger gamerule

If you attack the wither while the universalAnger gamerule is set to true, they behave differently. In survival the wither itself will not become hostile or hover above you after hitting it once while its small heads are attacking. It may closely relates to MC-29274.

To reproduce

1. Set universalAnger to true
2. Summon a wither
3. Attack the wither once
   → Notice that it doesn't hover above and towards you, but its smaller heads are still attacking.