There is a major bug in the quest-line, where the last time you fill up souls for the ghost, sometimes, more uncommon than not, he will just sit there even after filling the max amount of souls. It seems he does the animation where he'll start to float away, but it'll just reset and he'll kind of just sit there.

And it's extremely unoptimized, I've got a decent computer and the game lags 90% of the time. And unskippable cut-scenes.