As detailed in this reddit thread, the vitality and healing power bonuses of the rune set are bugged:
https://www.reddit.com/r/Guildwars2/comments/4k2164/superior_rune_of_the_druid_4th_set_bonus_is_bugged/
The 4th bonus doesn’t apply enough vitality and you lose the bonus healing power once you die, you have to reequip your armor to get the stats back.