Recent submissions of this item:

http://news.ycombinator.com/item?id=2826345 : 2 days ago - no comments

http://news.ycombinator.com/item?id=2825759 : 3 days ago - no comments

That latter item has the exact same URL except for a "#" at the end - I wonder if it was added deliberately to thwart the HN duplicate detector.

I did not know there was a duplicate detector now.

There has always been a duplicate detector. If you submit an identical URL, instead of a submission, you upvote the original version and get shown that page.

It doesn't always work, though. Sometimes it will still create a new post, even with an identical URL.

I suspect it only works for items in the cache, and anything old enough and not recently referenced might only be on disk and not get checked.