The quest for finding a Nervous Man in Tshibtin is definitely bugged, mine spawned off the far corner of the map... I can just barely see him, and shooting at him does nothing until I can speak to him (which I can't since he's outside the playable area). He always seems to spawn in that same spot, too... basically the only thing you can do is not take the quest in the first place, but at this point you'll just have to take a rep hit with whatever lord asked you to kill him. Good news is, I've only noticed this bug in the town of Tshibtin. All the others I've hunted Nervous Men in seem to work fine.