Actually, that's because there are two versions of the post -- one (this one) was crossposted to lj, and then got pulled back in when I imported my livejournal.

The reason that one appears in your reading list (not for long -- this is the version that has comments, so this is the version that is staying!) is because it's not backdated (I think DW has a different name for backdated posts, but don't remember what it was) -- as imported entries are.