Not sure if this is related to the Boss HP buff, the pet bug or just Vox's CH. I've had this happen 3 times in a row today (probably around 3 PM EST).

Class: Shaman
Level: 55-58
Mob: Lady Vox
Difficulty: Normal
Issue: Lady Vox fails to die; quest/chain XP is continuously awarded; no drops obtained
Notes: All 3 times I fought her and had this happened I had a pet out and she managed to get a CH off. The 4th time (I also had a pet here) I fought her she did not manage to get a CH off and died normally.

Video here

In this fight, when Vox was "killed" instead of dying she remained on screen and continued to take damage. This resulted in her HPs falling into the negative. Since her HP < 0, quest XP/ chain XP was rewarded on each swing/dot tick. (this chain increases since she remains "alive" and the combo keeps going)

Additionally, This did not happen on Phinny or Nagafen.

Is this still going on if you refresh? I patched around 5pm. I'm not duping it at the moment.

Refreshed and tried a few times. I was unable to duplicate it.

Thank you God. Thanks for reporting and following up!