Bug in Solo-Adventure "Book of Mercenaries"

During the Solo-Adventure “Book of Mercenaries” I encountered a bug, probably not that big of a deal, but still which ignores an in-game mechanic. During the second fight against Serena Bloodfeather, she used her hero power, which deals 3 damage to a non-random enemy and she targeted a Bearshark, which i got from the dwarvenloot, and killed it with the hero power, but Bearsharks ability is, that he can’t be targeted by spells or hero powers. Even have a screenshot, if I could include links :confused: