After hitting "Pass" for several heroes in a tactical battle, I noticed that the little shield icon that indicates a unit is defending was displayed right above the head of several of the heroes, but was much higher for one of them. The odd one is circled in red in the screen shot below, if you look closely you can see the shield icons behind the heads of the other heroes.
After trying this for several battles, I figured out that the misplaced icon is always for the hero riding the Umbran War Boar, and never for the other heroes who are riding horses.
