my survival world switched to creative

The game just switched one of my world's to creative.

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. ...the only thing I did different from usual playing was doing a WiFi game
On a completely different world.
3. ...