Category slug link in Post page

I notice if I have a post with multiple categories tagged, when I view the post (single.php, IIRC), it displays one of the categories, but sometimes it links the search to that category correctly, and sometimes it doesn't.

Is that a known bug? I could probably try to replicate on a public server version if it would be helpful. (I mostly been testing this theme use for an internal blog behind a firewall.)