Duplicate, most of the discussion is here: https://news.ycombinator.com/item?id=13165221
Actually, this submission was an hour earlier, and has the correct title and no url clutter. Yet for some reason the other submission got a lot more upvotes.
We'll eventually get around to working on a more sophisticated way of handling duplicate submissions, but the simplicity of the current approach (i.e. allow a few reposts if a story hasn't had significant attention yet) has much to commend it.