I tend to watch over the daily quest topics and let me explain why I've been slacking and letting 2~ topics at a time.
The PoE giveaway attached new members and spam. So the quest topics was getting pushed down to page 2+ (plus new people don't look very hard) so I figured why not 2 topics and increase visibility. When the spam slows down I'll start limiting it to 1 topic again.
*There was many many more quest topics I just kept the first 2~ posted.
Other times the topics are posted so close to each other (sometimes within secs) I feel like a ass punishing someone b/c there's no way they could of seen the other topic so I let them both stay and let the community post/pick which one they want to vote/post in.
*If the duplicate topic picks up speed (gets several post) before I spot it -> I tend to just lock those b/c I have no way of knowing if the first quest topic was on page 2/hidden (down-voted and listed for review) when it was posted.