Possession Bar - Drak'tharon Keep, Tharon'ja

[Song42]

So I can't seem to find a resolution for this one. Leveling an alt and ended up in Drak'tharon Keep, and on the last boss he does a possession, however by bar state never changes. I have the same bar mapped to Vehicle and Possess, and also with Overrirde checked. It has worked with everything else that I do/have done, and this is the first case of having an issue. I am unsure if this is maybe a bug, or there might be something I'm missing.