What is the ruling on someone who missed following the Imam in the prostration of forgetfulness because he was standing up to complete the rak'ah he had missed?

Scholars differed regarding the ruling on a latecomer (ma'mum masbuq) if the imam performs the prostration of forgetfulness (sujud al-sahw) after the salutation (tasleem). The majority (jumhur) held that he should wait for the imam and perform the prostration of forgetfulness with him, and then complete what he missed. They cited the Prophet's (peace be upon him) saying: "Indeed, the imam was appointed to be followed." As for the Malikis, they are of the view that he should not follow the imam, and his prayer would be invalidated by intentional following. Therefore, he should stand up to complete what he missed and then perform the prostration of forgetfulness himself. There is a detailed view from Imam Ahmad, as Ibn Qudamah stated in Al-Mughni: If the follower stands up to complete his prayer and his imam performs prostration (of forgetfulness) after the salutation, his ruling is like that of one who stands up from the first tashahhud; if his imam prostrates before he fully stands upright, he must return. If he stands upright but has not yet begun reciting, he should not return, though if he does return, it is permissible. If he has begun reciting, he should not return.