Elite bat spawned inside wall in Cathedral 2

Symptoms: Elite bat monster spawned inside a wall near the exit of Cathedral 2. It could not move to attack me.

Expected behavior: The bat would either have spawned inside the navigable portion of the dungeon or it would have been able to move into the navigable portion of the dungeon.

Steps to reproduce: Unsure - I have only seen this once and I don't think I can influence spawn locations from the client side.

I have a screenshot of the location where this happened but do not see any convenient means of uploading it.