There seems to be a bug with casting abilities that use fanaticism. As you can see from the video, the ruby states that "Sacred word can be cast instantly if there is fanaticism to consume". However, there is a slight cast time at the beginning of the spell, and moving will interrupt the spell. The same thing applies with Heavenly smite.
https://www.youtube.com/watch?v=T9TLxw5qgfE