Ask HN: Why can I upvote some of my own comments?

I was just browsing through some of my older comments, and I see that most of the way down the first page the comments cease having the asterisk in front of them and instead have an upvote link (the triangle).

I haven't clicked it because I assume it's a bug and I don't need to upvote my own comments.

The last comment with the asterisk was 33 days ago; the next one (first upvotable) is 48 days ago.