Hacker News Censorship
I upvoted it. Then I followed the link and read the article. When I wanted to come back and read the comments, the post was nowhere to be found. I checked my upvoted stories on my user profile, but it was not there. I checked the HN search function for the article, but again I could not find it.
So I thought that perhaps I had imagined finding the link on HN. So let me post it on HN since it is interesting. But when I tried to post it, it said "This story has already been posted"
So I wasn't imagining it. I repeated my search again, but I could not find it anywhere.
After that I purposefully reposted someone else's link and got no such message that it is a dupe; and it successfully posted.
Try it out for yourself. Try to submit the link above, and try to post another dupe and see what happens.