all i can say is that its different for everyone no particular quest or anything is responsible its just the game it self.Surprisingly the game ran flawless for me other than the minor glitches of course but none that prevented me from playing the game or finishing quests and etcetera..
but when i got the patch an hour after that my game went haywire and it all went to hell from there

even without the patch people still encountered the same game breaking flaws.
so i guess we are all just screwed from the get go