Mana cost efficiency anoint is increasing mana cost instead of reducing it

I have an amulet with Efficient casting, which should lower mana cost. Instead my mana cost is going up by ~3%.
This only seems to be the case for anoints, I have a mana cost efficiency notable on tree which works fine.

Screen recording, play at half speed -
https://www.youtube.com/watch?v=fA7HtmCl4rg