I have noticed that since the Necrom patch, the "Kill 20 XXXXX" quests seem to calculate much differently than before, especially if you are in a group.
Previously, you could pick up the "Kill 20 Enemy Soldiers" quest and expect to complete it rather quickly. If you were surfing the zerg or in a zerg group, you could complete it during the next fight engagement.
No longer.
I have joined a lot of groups since the expansion's release, and have gotten Kill 20 Enemies shared to me. Some of these groups have been 5-6 people total, other times the full 12. After being in a 12 man group for 2.5 hours, I had 5/20 enemy players completed.
Initially I thought maybe it was because I was on a healer, so I brought out a brawler and made sure to get hits in. No consistent progress.
Then, maybe I thought I just needed to do the majority of the damage to a player. Still no consistent progress.
Next, I tried getting the killing blow on the enemy players. No consistent progress.
Finally, while in a 12 man group, doing the most damage (in some cases, ALL of the damage), AND getting the killing blow on enemy players, I would often not gain progress on my Kill 20 Enemies quest.
I have found this to be the same across ALL the kill 20 quests when grouped, not just the enemy players. I used the kill 20 enemies as my example since previously it had been the easiest to complete.
Before I made this post, I decided I should try some solo tests - one where I was solo with no group members and no other alliance members around, and another solo and zerg surfing. In both these instances the killing blows DID count towards Kill 20 Enemy Players completion when I was ungrouped.
Additionally, when I was stacking with my alliance it appeared I was getting credit for kills which didn't even count in my Kill Counter addon.
For example, before I went into a fight at Nikel, I was at 5/20 players. After the fight I had a kill streak of 8 with 3 killing blows and when I checked my quest, I had already completed it. It appears I got credit for 7 additional players that didn't register on the kill counter for a total of 15.
Is this an intended change to penalize people for joining groups?