New mobs dosen't despawn in peaceful :/

Put the summary of the bug you're having here
New mobs dosen't despawn in peaceful :/
What I expected to happen was...:
I expected they will despawn like other mobs .

What actually happened was...:
They didn't despawned

Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ...
3. ...