I wanted tunnelers' dream preset with 20 stone block instead of 230 and i clicked create so i thought it would just be normal and everything..

But now there is a abandoned mineshaft with mob spawners etc. everywhere it happened to my friend too when i explained it on skype

Steps to Reproduce:
1. make a new world in creative mode
2. choose superflat
3. choose the preset tunnelers dream
4. make the amount of stone blocks 20 instead of 230
5. play your world and you see what happened