Huge Chunk Error

I had an idea for a build I wanted to do. I did not want terrain to get in the way, so I generated a superflat world.

What I expected to happen was...:
I thought there simply would be a large open space, or "superflat".

What actually happened was...:
It's hard to describe...Right next to the land I spawned on, there were chunks in the middle of the flat land. Some stood alone, others in groups, like chunks poking out of the ground. A sideview of caves and mineshafts were visible. At some points this glitch prevented water and lava from flowing, but other time it ran freely.

Steps to Reproduce:
1. Generate Structures is ON on the creation menu
2. Before generating the world, I clicked on the superflat layer edit. I did not change anything, but it was the first time I noticed that option so I clicked it.
3. No seed. I don't know if you CAN, in fact, reproduce it. I may be able to get a seed for you. I have included pictures for a better description. (the screenshots I took were not in my library, I apologize in advance...)