So I just noticed that each time my vampy is well fed, vampiric seduction disappears from my powers and favorites as well. After some days of not having drunken blood it comes back, but I have to reinstall it into my "favorites" each time again, which is annoying ass f...
Which genius at Bethedsda thought this would add to immersion?! So...is there any mod already that fixes this or else would someone volunteer to make such a mod?
It occurs because the power is requires you haven't feed in a day. I don't think I have experienced your specific incident of it resetting in favorites, but I wouldn't be surprised.
Anyway, turbosnowy has a mod out that changes it http://skyrim.nexusmods.com/mods/23155. It also makes it target scale up significantly more, so you can use it to feed on your followers more readily.