Your experience is different than mine.
If you select Export > Selected Individuals > Ancestors
You are given a screen which gives choices:
1) How many generations up to 999 generations.
2) Whether Preferrred spouse or ALL spouses. (but not ancestors of any of these spouses who are not ancestors of the selected person).
3) Descendants of all of these ancestors - up to 15 generations from each ancestor.
My experience is that these choices will NOT result in ancestors of spouse(s) of the selected person in the report nor who are not ancestors of the selected person.
Suggest you try again.