Calling @dang ...

(URLs can't be edited by non-admins like me)

Assuming you submitted the actual URL, it's a canonical link problem:

  <link rel="canonical">

That's the canonical link in the page, which points to nothing. Which I'd guess HN rewrites as just the root (what is currently being pointed to).

I used the bookmarklet, and it's plausible that I was, at the time, viewing the blog root page (as linked here) rather than drilling down to the permalink.

So it's likely to have been my mistake.

Edit: I've emailed the mods.

Edit2: It's been fixed.