In the battle against undead near the church, Jahans health bar looks strange. I have 534/534 HP, but the bar looks almost empty. When combat ended, the bar became fully red again.
Not sure it is a bug. I wonder if it has something to do by you setting up a path directly through a poison cloud and an area on fire. Maybe the light red portion of the health bar is the amount of HP you will lose if you go through all those hazards. This is just a guess, I have not verified it.