The boss for this quest used a LOT of combust, which reminded me of a similar bug I ran into with the old trolls quest and the hagwitch spamming too many Ice Storms. I couldn't give you an exact count but there may have been at least 15 combusts- this may need to be looked at.
He is a toothless wimp without infinite combust.
It isn't a bug. He is intended to spam combust.