I recognise the phantom casts. it even reset when we did it with a group the first time. We had to redo it, and managed to take him out faster.
It's strange cause you are not death but you are, even typing /stuck does not fix it. only going outside and back inside kills you so you can respawn...
The 2nd part is I think something he does. sometimes he has a special ability that makes you move diff. it's only so long.