If serana gets low on health and takes a swig of a blood potion from her inventory after the player has cured their vampirism, the player partially becomes a vampire again. By partially, I mean he/she starts taking sun damage again and gains vampire spells. I can not transform into vampire lord again and the race doesn't change back either (eyes dont start glowing) . It appears the "PlayerIsVampire" global is not changed to true. Which is maybe a good thing as that is how one can code and figure out if the bug has occured.

I spent all day trying to figure this one out. Why I was randomly becoming a vampire again durnig fights with Serana. Figured out that it was happening when serana would get low enough on health to take a swig from a blood potion.

I dont know if this bug was introduced by DragonBorn or not because I didn't give her blood potions before this latest run through.

Patch Version: 1.8.151.0.7
DLC: Dawnguard, DragonBorn