OpenAtlas

One has to enter both, the Administrative unit and the Historical place in one editing.
If on of the two (e.g.: Administrative unit) is set first, the data saved and then the other (e.g.: Historical place) is edited and saved, the first data (in this case Administrative unit) is removed.

E.G.: For "Istanbul" the "Administrative unit" is set as "Turkey" and then the data is saved. Later, the "Historical place" is set to "Ottoman Empire" and the data is saved. The entry for "Istanbul" will now only feature "Ottoman Empire" as the entry for "Historical place" and "Turkey" as "Administrative unit" will be gone.
If "Administrative unit" and "Historical place" are both set and then the data is saved, both will be present.