I was out foraging for materials and I noticed a melee involving several players and enemies. It was cool to watch, so I wandered closer ( assuming I was too far away to actually help out before it ended). As I got closer, the players prevailed. Then a quest message flashed on my screen saying I had completed the quest - just because I was in the same area.
Now I'm annoyed. If the quest is marked complete, then I don't get to do it, right? Is there a way to 're-open' a quest? I want to try it myself (it's a good one I think, with a boss fight at the end)