Mad Druid in Pikataclysm has permanent Cauterize

[Planetus]

After getting into Pikataclysm on my paradox mage and facing the Mad Druid for a bit, I noticed he was perpetually at 22 HP. Then I noticed that he was also perpetually at Cauterize(9). Then I noticed that all the attacks I was doing to him were doing 0 damage, no matter what the damage type. I'm assuming this is a bug. He is still active and attacking.