NPCs fall through stairs in Balmora

In v0.32 I have seen NPCs fall through staircases and get stuck in them in Balmora. I have attached the saved games where you can see them stuck. Unfortunately I do not know what caused them to fall through and was not around when that happened.

(RM-2007 from redmine: created on 2014-10-11 by Sergey "Shnatsel" Davidoff, , closed on 2015-04-01 by nobody, relates #1867 (closed), duplicates #1587 (closed))