A Question Regarding an Answer in the Guiarati Edition of Fataawaa Raheemiyyah

Q: Salaah-89: Please explain the ruling below in the light of authentic references. The extract quoted below from the Gujarati edition of Fataawaa Raheemiyyah (Vol.1 Pg.86) conflicts with what another book states. Which is correct? Here are extracts from both books:
From Fataawaa Raheemiyyah:

Q: Salaah-90: The Imaam forgetfully omitted a Waajib act in salaah and also forgot to perform the Sajdah Sahw. The salaah therefore needed to be repeated. Now will the salaah be valid of a person who joined the Jamaa'ah only when the repeated salaah was being performed?

Answer: His salaah will be invalid and will have to be repeated because the second salaah of the Imaam's is not a Fardh salaah in its own right but a completion of another Fardh salaah. It is not correct for a person performing a fully-fledged Fardh salaah to follow an Imaam who is merely completing an incomplete Fardh salaah. And Allaah knows best what is most correct.

Fatawa Rahimiyyah vol.2