I've e-mailed in an exception log but thought I should at least mention it here in case someone else runs into it.

The Yor have been at war with the Altarian Resistance for most of the game and have been steadily winning. Eventually they must have become so powerful that the Altarians gave up, because their leader portrait popped up saying they've decided to surrender to their enemy.

Now since I had a mutual research treaty with the Altarians, I decided to bring up race stats to see what had become of it, and that's when I got the exception.