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Again, for me Patrick never gave me the Dragon breastplate quest... That is a BUG, not a quest failing for a reason...

If you got the quest from the Dwarven King (I'm assuming you did?) and go to Patrick, there is one sentence that busts this quest.

http://www.kiya1.de/images/Div_Drag17.jpg.html

as I'm coming from the adventure side, I'm used to reaction/consequences as Flash has described it. So, you could call this "killer sentence" (my choice of expression) a bug or (in my case) consequences that occur by fibbing - and Patrick even warns not to lie to him. What I don't know in this case is the Larian intention though.
Kiya