Ask HN: How fast can a post go down in ranking? 400 ranks in an hour?

The post I'm talking about is this: "HTML7 magic on Facebook" http://news.ycombinator.com/item?id=3922402 It came up to Rank 18 at one point and in the next hour it quickly tumbled out of sight all the way to rank 455. Is this possible? The last time one of my posts hit the front page, it stayed there for at least half a day. What's going on? Is this some evil conspiracy to keep the news about Facebook using HTML7 away from public knowledge? :)