[douglas]

This is a known bug. If an emotionless race acquires a planet that is rioting, it will never stop rioting because the happiness change step of turn processing is completely skipped for that race and the initial rioting status for some reason overrides the emotionless trait. If you have a trustworthy ally who is not emotionless, you could load it with troops and transfer it to him just long enough for the rioting to stop. Another option is to load all the population into a transport, kill the last 1 million by "abandoning" the planet and not scrapping facilities, and then drop the population back on. Abandoning the planet without scrapping facilities results in a 0-pop colony with no happiness rating at all, and happiness is reset to the default for a new colony when you put the population back.