» Sat Jun 09, 2012 4:34 pm
I think it's a bug....I have killed 119 dragons, and only one failed to give up a soul. The failure occurred at the tower, just west of Whiterun.
In my experience, the word wall/lairs will respawn dragons until you reach a certain point in the main quest. I'm not sure what that point is but I left the main quest at Diplomatic Immunity, and went adventuring, returning to the lairs every few game days to slay more dragons, and collect more souls. Once that point is reached in the main Quest, the dragons will stop spawning at the lairs, and will start attacking you in the cities, while leaving dungeons, and fast traveling anywhere. This seems to happen (for me) about every three game days.