It seems that the code for the health cost of Health Funnel is flawed. Instead of doing currentHealth - (.01 * maxHealth) it does setHealth[currentHealth - (.01 * maxHealth)]
What this means is that on fights like Nefarian or Chimaeron, you can exploit it to avoid massive damage/stay alive. It requires some timing, though, but it's not super hard. As long as your tick happens within about a quarter of a second of the damage, it'll "heal" you back up. Note: I'm not quite sure whether it's before or after the damage, it's hard to tell.
If you want to test this, you can do the reverse. Simply create a Healthstone, start Health Funneling your pet, and pop your Healthstone right around the tick. It might take a few tries. You can also do it with Life Tap and Health Funnel, but I found that harder to pull off.