This is intended HN behavior. Someone else submitted it again today and due to the closeness of times (within a few days), a new item is not created but the old item is boosted.
Ah, thanks for clarifying, did not know this. I thought when someone submits an existing link it either has no effect (and the submitter is redirected to the old post), or a new post is created if enough time had passed since the original submission.
