jennur's horde bug
hahahi20
today, i tried to complete jennur's horde whit master reward, for the reward i made a hit and run on the two harbringers on the bridges with a light of serleborim, killed them both but left the group alive, but at the end, when i killed the harbringer of nightfall, i only got the normal lowest reward not even expert, saying that i killed 0 of 2 extra harbringers
Dzjudz
Yes, this is documented on the wiki page (both in the bonus walkthrough and as an Anomaly note at the bottom).
IronSheik
Not a bug, have to kill groups as well.
Divine Ashes
Yeah, you pretty much answered your own question with your OP. You have to kill the groups along with the Harbingers. This is documented on the wiki and isn't a bug.
Sierraa
We do have a section called Game Bugs. :]