/PET GUARD
 

Apparently, when pets are on guard and come back from killing a mob... they are prone to fall through walls and/or the world. They then fight whatever they encounter and, after they die, they leave you with a massive train.

I've had this happen in Seb, HS, and KC.... but I'm sure it's not exclusive to just those zones. It happens only when using the guard function. Pet follows find and never does that on any other setting.

I've also seen this in HS, near the safe hall in South wing.

Had it happen to me a few times in certain zones. Just have to be mindful... and self CoTH when needed.