Re: Playing with fire bug, it could be mantle.
I'm also using a human warrior and this quest is broken for me.
The pillar has vegetation that gets in the way, it seems?
Also, my card is only capable of running the game in Direct X 11, I don't even have "mantle" as an option.
Edit: User Yentsee found a fix for this quest: Circle the statue on horseback 3 times and it will work. Seems to work every time.