Currently working bug in DD allows you to enter earlier (before the event starts) and clear the dungeon, and after the event starts all you have to do is relog. Game thinks you entered after the event so you get the extra chest. This way you will probly get 4 dungeons chests extra with a good group.
http://www.reddit.com/r/Neverwinter/comments/1elnr2/info_dungeon_delves_bug/