Derth über shops. Reward, or bug?

[martinuzz]

After killing the Gwelgoroths in Derth, but before leaving the town (in other words, when the cloud is still hanging over it), the shops in Derth have been transformed to super shops. I could buy level 5 gems (fire opal, diamond, etc.), and also high-grade material armor and weapons.
I always thought this was normal, some sort of semi-hidden reward for saving Derth, but now I'm told that it is a bug.

Anyways, please don't fix. There is no other direct reward for saving Derth. I think it's a cool reward. At the time of the Derth quests, most players won't have enough cash anyway to really exploit this.

[darkgod]

The reward for doing the quest is killing urkis: guaranteed exp + artifacts