Put the summary of the bug you're having here

What I expected to happen was...:
I was playing in superflat, expected in the f3 menu to show superflat or at least plains under biome

What actually happened was...:
It said I was in an Extreme Hills biome

Steps to Reproduce:
1. Make a new world in superflat
2. Open f3
3. Sometimes it might appear Extreme Hills in biome