This started before I got through the first gate at Portcestre. Since I had a handful of flaming arrows anyplace there was oil would catch me on fire. I had a helluva a time getting through the first door because ever time I would get close to the battering ram I and everyone else would catch on fire. As you can see here late in the quest the problem persisted and wouldn't go away until I made a save, quit out of the game and reloaded.