[throwaway32]

they are marked dead on a post by post basis, unless (i believe) the account has a history of only posting spam links.

In this case, your link is a duplicate of an earlier/more popular post. So it got auto-deaded

[mrpixel]

Uh? Is that new? Whenever I posted something already there I got diverted to it. And I believe the older submission got an extra point. That was cool.

Maybe it's different when the older post was marked as being dead? But I hope there isn't such a lack of humour on HN.