Editor: Editing a reference's position after loading an esp file makes the reference disappear

There are some issues with cell references at the moment when converting an esp file to an omwaddon file. For example, editing an instance's position causes it to disappear from the Instance table. I suspect the Dark Brotherhood.

(RM-3514 from redmine: created on 2016-08-30 by Kyle Cooley, , closed on 2018-05-19 by nobody)