Via Hearthstone: http://ift.tt/2oJlZjM
The text of Amara, Warden of Hope (the Priest quest reward) is identical to that of Alexstrasza, the only other card that directly sets a character’s health. Amara, however, does not have the same effect: instead of directly setting your health to 40, she sets the maximum to 40 and then heals you by 40 points.
This means that playing Amara onto a board with Auchenai Soulpriest already present is suicide. Don’t repeat my mistakes.