What is the ruling regarding the followers (Ta'ifa) who are praying behind an Imam when the Imam makes a mistake (sahu) before they separate?

Primary text

If the Imam makes a mistake before the separation of the two groups, the ruling concerning the Imam's mistake applies to the first group of followers. If the followers make a mistake before separation, the ruling concerning their mistake does not apply to them because they are considered followers (ma'moomun).