(I'll try to update this as I discover more to tell about these bugs)
Animals tend to act quite unusually with sleep when it comes to a world with perma-darkness set.
- Pengulls will let you murder the entire pack with next-to-zero repercussions
- Beefalo can occasionally "detach" from the herd (despite still being in the herd) and allow you to single them out without the others coming after you. We're talking attacking them right in front of the other beefalo (while they are in heat), no kiting, gimmicks, or other antics. I don't know if the sleep flag is overwriting something, but they stop acting predictably and I'm not really sure if the behavior ever reverts.
Steps to Reproduce
For Pengulls, let them come into your world and fall asleep. Attack one shortly after and one might wake up to attack you while you are finishing off his buddy. As soon as you lose aggro, start attacking again, none will fight back. One or two might wake up, but they won't actually fight back. I'm not quite sure what happened for the Beefalo version, but for now I will note that this seems to happen most commonly when they are in heat.
This issue has not been confirmed by a developer yet.