Hi I was just going to the golem forest and I jumped down on the last platform in Sleep Dungeon I. It didn't teleport me to the next map and there were a good amount of enemies spawned underneath. Was an odd thing to experience.
This was in the vanilla game as well. Back in the day if you didn't go all the way down the ladder you could jump off (This was before jump down was a thing iirc) I don't know why mobs are set to spawn here, but they do. If you go up the ladder you'll hit the loading zone and spawn on the next map.