
The buggiest is when I exited the scen, I could still see damage numbers on the left top of my screen. I guessed it was some of the players who still had the buff and fought somewhere (scen or ORvR). I was getting credit from their kills no matter I was not close to them and I was in combat whenever they were.
I am pretty sure the same thing happens with BW buff or any other damage buffs. I could theoritically be afk and for 1 hour get credit from the players I had buffed.