According to the wiki, both of these curses are supposed to make healing do damage.
Curse of Narfell: A Cursed creature is harmed by healing spells as if they were undead (and yet not healed by inflict spells)
The healing is only prevented and does nothing(Only had access to Cure Light/Moderate/Serious/Critical Wounds scrolls and potions).
Inflict scrolls still do damage as intended.
Curse of Red Death: Damage over time, healing magic damages, inflicting cures.
(I could only test this one on PGCC)
The healing is only prevented and does nothing(Only had access to Cure Light/Moderate/Serious/Critical Wounds scrolls and potions).
I did not see any damage over time.
Inflict scrolls did heal as intended.