'ignore_automatic_features' does nothing

When creating custom biomes, adding the object: "minecraft:ignore_automatic_features": {} does nothing for the generation; dungeons, broken portals, mineshafts, etc. still spawn. Is this object broken or is it meant to do something else?

 

Steps To Reproduce:

1. Download, install and start a new world with the supplied pack (experimental features on)
2. Setup a ticking area around a command block that runs the following command

   /execute @a ~ ~ ~ fill ~-4 -60 ~-4 ~4 70 ~4 air

1. Move around the stone biome, eventually you'll come across a mineshaft, dungeon, broken portal etc. (See picture)

Expected Results:

• ignore_automatic_features disables the spawning of default structures like dungeons, broken portals, mineshafts, etc.

Actual Results:

• Nothing changes when this object is added or removed