I think the Duncan quest needs a complete rewrite. Currently, the player can get the 
reward only if he has never met Koan. Then, the player can only choose between 
outright evil or spare naively. Finally, Tux never get a clue about Koan or the 
cube.

In my opinion, the correct solution is to expand the quest by allowing Tux to help 
Koan. By example, faking the death of Koan. Or providing Koan with some means of 
defense. In any case, Tux must have terminated the quest with Duncan before he 
receive the reward of Koan.

So, I prefer to spend more time of the quest after the 0.16 release. I think we can 
live with this bug. If everybody agree, I will lower the priority.