WX - Poisoned

I was playing WX, and ate Tubor. He is immune to poison so i thought there won't be problems, but WX got poisoned, but he wasn't loosing any HP, but the arrow pointing down was still visible at the heart icon, but senity drain was normall (Even though I play as WX who is supposed to be immune i still got poisoned, but only the sanity drain remained and not HP drain)