I was just aware of a bug today when I ran EN VoN3 (Jungles of Khyber) on my TR.
I did get the first time bonus as expect, but on the second run I looked at the XP sheet and saw a -90% for repeating the quest 10 times.
I did repeat it 10 times, but that was on Heroic difficulty when I was around lvl 10.
Is this one of those U14 bugs that have been around for a year and still not fixed because Turbine is working on flying cat companions? :(