A heart under a post briefly showed a like count of minus one — the server always had the right number, but the copy on screen was doing arithmetic on stale information. The cause: a post can be on screen in more than one place at once (the timeline, its own story page), and when likes changed, only one of those copies got the news. Now every visible copy of a post updates together, and the count on screen can never go below zero. (Theme v0.5.307.)