Mobs are able to spawn in the Deep Dark city

Hey Mojang!

While I was testing out the recently released Deep Dark snapshot, I teleported to an ancient city and changed my mode to survival. Within a few minutes, three zombies and two spiders were chasing me.

 

As you guys once stated, mobs should not be able to spawn within the Deep Dark biome/city. Perhaps this feature wasn't added in this snapshot.

 

Expected Result

• Mobs should not spawn in the Deep Dark biome or the city.