Well. I just failed a quest today that I hadn't even begun.
Picked up the 'quest for a cure' and right after I had left the room (still in the zone, but around the corner and unable to see the doctor) someone else turned in the quest who had been unable to retrieve one of the plants. It updated my quest as well, apparently due to my proximity.
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Aparently is not only when you are nerby, if you take the quest and someone else finishes it before you do it marks it as if you had resigned. It happened to me when i was in another area, so i dobut it is a matter of proximity.
I've only observed this on "A quest for a remedy" quest though
Somebody who's doing the scripting on this needs to use the unique number generator and slap that onto the quest handler so there's a way to differentiate between quest instances.
Been busy but I will check it out.
Why do you get angry at the new system, once this is just a bug that is not intended to be part of the system, and will soon be fixed, a little patience there, awesome things like this need some adjustments after implemented, that's all.