Alright, this is primarily about the great northern wall mission, but it probably applies in other places too.
When you open the wreckage for Kinn Testebrie's armor, its assigned to a random person in the party, like any other container. If you have henchmen though, sometimes apparently the drop will get assigned to them, and thus you will not recieve a quest item necessary for the bonus. This wouldn't bug me too much, as its very early and very easy, but I was on with necro one night and didn't really feel like getting a group together, hadn't done the bonus so I went for the 1000xp, and I had to re-do the mission 3 times before I could get all the armor. It didn't make for an enjoyable experience one way or the other. That definitely sounds like a bug to me, don't know if anyone else has noticed or been annoyed by it, but supposedly ANet reads this stuff, so here it is.
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Basically...I think that the four pieces only drop when the group are real people...this has once again happened to me on the "feed joe" quest in the shiverpeaks. I did it with hench and not enough roots dropped, however, when I did it with real people, every piece dropped as it was supposed to...mabey this is just a henchie glitch? who knows....I wish they would change it, and also not let hench suck gold from the "shared" when you pick it up 