Lower Guk Pathing (Spider tunnel)
 

When you pull these mobs you have to babysit them inch by inch so they follow you or there is a good possibility that they will turn around and go a completely different route to get back to you. I've seen what looked like 20-30 mobs come back as a result of this pathing error. Even if you're a really good puller, it can still happen (and does) quite frequently.

It's pretty hazardous to groups at the bedroom area.