We just went to do some more practice runs and at the beginning of every run (around the 18 minute mark) he starts healing up to max HP (I can visually see him healing various amounts between 1-2m, but it has to be more than that since it keeps him at full HP).
If it helps, we're using an F/P, Xenon, Paladin, and we just started using a Bishop for Heaven's Gate. He didn't do it yesterday when we didn't have the Bishop, could that be causing it somehow? I really have no idea. Has anyone run into this? Does anyone know what might cause it?