On an additional note, demon hunter will frequently display 0 hp for the user (but sometimes show the correct hp from a party member's point of view) if the demon hunter uses smoke screen on what would have been a fatal blow. The result is that the demon hunter will no longer be able to know how much hp he or she has.
Receiving any heal from any source does not fix the display, only taking non-fatal damage does the bug fix itself.
If the user attempts to use a potion while the demon hunter is at full hp (while still displaying 0 hp for the unknowing user) the potion cooldown will reset while no potions are consumed.
This is very frustrating as this happens frequently.