Kireek

[Cye Zero]

Faltz can't control you character because (I'm going by the story, ok just a hunch)your character is to strong to control. All of the people who Faltz controls or abducts in the various ruins quests showed some kind of fear while they were down there. I'm not exactly sure how this effected Kireek, but maybe with the lose of his rival he feared that he no longer had a purpose or a reason to fight. Anyway since your character is to strong to control Faltz tries to eliminate you.
The only time I've seen the possession work (sort of) is in ep.2 when you fight Olga Flow. I guess it works because Flowen is stronger than your char.