Succubus is a beast. Stealing a unit triggers her beastly maneuvers again. But I guess that's not the way it's suppose to work. You can contact support and let them know.
Since this thread is about Succubus, I dreamed an extra 'r' letter in 'beastly' upon first reading the phrase. Maybe a similar thing made Berserker Maurauder to go into a beast mode.
Played Succubus, after 2 turns took opponent's Geralt and a Harpy from my deck flew on a battlefield, though Geralt isn't a beast. Saw that exactly report in the "[bug] harpy" topic here.