Reverse Bug

Put the summary of the bug you're having here
When ever I build something in creative or survival out of the new blocks and you exit out of the world then come back its all gone.
What I expected to happen was...:
Describe what you thought should happen here

What actually happened was...:
Describe what happened here

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