Every time I do it by just camping and resting outside, I don't have any problems, but if I use the inn to rest overnight I usually do. Never had that happen before, but with repeated spawns it seems to be pretty consistent. I absolutely verified that at least a couple of the dragons were regenerating hitpoints overnight if I rested at the inn. I'm actually getting kind of irritated in Paradise Valley. I've had to do all my training there for a while (level 318 now) and it seemed like it respawned every time I turned around.
