Chewbacca issues?

Today in GW I used chewbacca to taunt. He was at full health, and I have the upgraded taunt that gives you more HP. Well when I hit it, it went on cool down, I got an at full health icon above his head, but no taunt. I then proceeded to lose two heroes and subsequently the rest of my team. A little frustrated, and a little disappointed. Is this something other people have noticed? Am I now unable to taunt with him if he is full health?