I post a lot of links to HN. It's a hobby - I have lots of RSS feeds in NetNewsWire.

Double posts do happen, HN's algorithm allows it. Occasionally a post that got little attention will get boosted up to the front page after a few days.

But I didn't post another copy of this link a few hours ago, and I've never had HN create a duplicate post way later - no clue what's going on here...