Strange generation in Debug Mode Nether

Put the summary of the bug you're having here

What I expected to happen was...:
The nether would be a void in this world mode

What actually happened was...:
All blocks from debug mode transferred to the nether, random lava islands and spots throughout the dimension

Steps to Reproduce:
1. Enter debug world
2. Exit and re-enter debug world
3. Find the nether portal block and enter whilst in creative mode