Social Zombies spawning in well lit areas during the day

I have a castle for a base, and it's not finished so there's no ceiling. So during the day it is incredibly well lit. But zombies will start their 'social zombies' thing and spawn 10 blocks above the ground inside my base. This happens constantly. Also, I have an Iron Golem in the base and he never attacks zombies that are a part of the social zombies crew.