I completed the quest, but there was nothing in the chest which was open already when i entered the reward room. Dunno if it's a bug or not.
Same bug but the chest was closed when I entered the reward room.
Its a bug pretty common to reward chests. I've got no idea what triggers it, though I always feel its a good idea to try and make sure chests are closed before you leave a quest area.
I think it's normally caused by lag. It happens on a number of loot placeables around the server.