Wither boss do Idle moviments when his health bar is at half

Steps to Reproduce:

1. Spawn a wither boss in your world
2. Do damage to him until his health bar is at half and he gets wither armor
3. Put a target to he attack in this phase

Observed Results:

Wither boss still attacking the target but he do Idle moviments (Jumping around) 

Expected Results:

Wither boss should attack the target in attacking position  

 

Device:LG K10