Recently I decided to plant a whole bunch of wildberry bushes (about 90) next to each other since with Pam's Harvestcraft they're one of the most time-efficient foods. However, as soon as I did, I started to notice that 1-2 witches, 1-2 zombies, 1-2 skeletons, and 1-2 endermen would spawn during the daytime when I started to harvest them. I'm not sure if this was a bug, but after removing the bushes those mobs have stopped spawning.