All of the quests stuff is bugged. Quests keep disappearing and re-appearing when re-loading the game; quests can't be completed because objectives aren't flagged as achieved; quests suddenly appear and disappear; rewards aren't given. The list goes on.

In my most recent game, from what I can remember:

Pyre of Man: Attacked his stack, he did not appear on the tactical map(His army did), when the battle was over he disappeared from the strategic map along with his army, and now I can't finish the quest.

Scrap Golems: Mid-game Scrap Golems spawned around one of my cities as part of some quest(Although the quest icon did not pop up until later), but they spawned on top of mountains and in the sea. The quest appeared and then disappeared later, and after finally killing them all with Firestorm or whatever the strategic map spell is, nothing happened.

Snake Elemental(Can't remember name): Upon entering tactical combat he will have the first move, but won't do anything. Have to auto-complete the battle. You only sporadically get a trophy(This applies to all the Elemental Lords).

Numerous smaller quests don't give rewards on occassion, I have two quests on the map that can't be finished because of some bug, all kinds of stuff. It's a mess right now, really.