0.6.8 Aeolian Fight Bug?

I can never seem to damage him… Perhaps I do not understand the effect properly.
He became vulnerable to sorcery, so I cast Morph: sorcery, and then attacked him with my creatures.
None of the damage had any effect… it was all prevented by the boss trait.

And spending a long time waiting for the class to cycle through, none of my spell or attack damage had any effect…

The effect is definitely bugged. He ended up taking damage from Battle from Within, which is definitely damage that does not come from attacks or spells.