Lush Caves and Dripstone Caves continue to generate mobs despite being on a Mushroom Island.

In my world created in this snapshot I appeared in a giant Mushroom Island, the problem was that when I went down to the caves and saw that I was in a Lush Cave, it generated mobs even though I was in the big Mushroom Island. Personally I think this doesn't make sense since the whole point of Mushroom Island is to have a small (or not so small) piece of world where no hostile mobs are generated (not including spawners obviously), so, if when I go down to the caves mobs start appearing the point of this is lost. I'm on a Mushroom Island and I still have to be protecting myself from hostile mobs when it should be a quiet place. Seed: 6831652595494821701