Quest ransack

Quest Ransack, as introduced in Update 19, is a stacking penalty for repeatedly playing the same quest. You may play each difficulty level once per character, per incarnation without incurring Quest Ransack penalties. After that, each playthrough will add a 20% stacking penalty to base XP, up to a maximum of -80%. 18 hours after the most-recent completion the penalty is reduced by 50% (and again 18 hours after that). This 18 hour timer restarts each time you run a quest, so if you never leave a full 18 hour break between runs, you will always have some penalty.

You can check your currently penalized quests by typing the /ransack command. If used while inside a quest, this command will also tell you which optional objectives were already completed in the last 18 hours, and their personal penalty.

Note that end reward lists will not include Commendations of Valor if you have any currently active ransack penalty for that quest. In effect, this means you can only complete any individual quest for Commendations of Valor once/day (actually /18 hours).

Example
Day one: Day two:
 * 1) Elite, first time completion: full exp (0% ransack after run)
 * 2) Hard, first time completion: full exp (0% ransack after run)
 * 3) Hard: full exp (20% ransack after run)
 * 4) Hard: -20% quest ransack penalty (40% ransack after run)
 * 5) Hard: -40% quest ransack penalty (60% ransack after run)
 * 1) Hard: -10% quest ransack penalty (30% ransack after run)
 * 2) Normal, first time completion: full exp (30% ransack after run)