[neilv]

Falsifying timestamps is a kludge that HN uses when moderators give a post a second chance to gain traction on the front page.

(Personally, I have a strong aversion to falsifying public information like this, and I hope that they will prioritize implementing this better.)

[gblargg]

This might explain why I see a post, then have trouble finding it the next day. It sounds like it can move around in the order of things.

[neilv]

That might be a different mechanism.

Unlike Reddit, the ordering of HN posts isn't only a function of the numbers of votes, number of comments, and time. Some other moderation activity can cause a front page post to suddenly be buried many pages deep.