In the overworld superflat preset (which is a plains biome), there are many different structures from other biomes that should not be generating. This includes Desert temples, Jungle temples, Igloos, Witch huts, Shipwrecks, and Underwater ruins. They are also generating at very high rates relative to a normal world. So far I haven't seen an ocean monument or woodland mansion but they may also be present as well.

What I expected to happen was...

None of said structures generate in this preset. Only Villages, Dungeons, Strongholds, Mineshafts, and Ruined Portals should be generating.

What actually happened...

Said structures are generating in this preset.

Steps to Reproduce...

1. Create a world in the snapshot using the Overworld superflat preset.
2. Look around to find all the structures.