Multi Noise biome parameters do not accept values higher/lower than ±2.
So if you put in a custom world JSON file, for example 3 (humidity, temperature, weirdness or altitude), game will generate the classic vanilla distribution. Fixing this would improve the customized worlds and it would help balancing these biomes if creator wants the biome to be rare, for example.
That's an invalid configuration, as the log file will tell you.