Hostile Mobs spawn in Peaceful / broken difficulty setting in Realms

This is at least happening on Realms.

Hostile Mobs spawn when in Peaceful mode, switching to Easy/Normal/Hard and then back to Peaceful also doesn't despawn hostile Mobs.

Video: https://www.youtube.com/watch?v=82p_SnzmuMA

Edit: I download my Realm today and noticed that the downloaded copy had difficulty set to "normal" (The Realm was running on peaceful the whole time). Switching the downloaded copy to peaceful and uploading it to the Realm solves this issue, until you switch to another difficulty again.