What is the ruling on an imam who adds to the prayer out of forgetfulness and does not heed the reminders of the ma'mum?

Question:
He says: We have an imam of the mosque who sometimes adds to the prayer out of forgetfulness. When the ma'mum remind him by saying "Subhan Allah," he does not return if he has already begun to stand up. It is known that he does not say takbir after rising from prostration except when he is standing.

Answer:
If he stood up for an extra rak'ah, a fifth or fourth in Maghrib, or a third in Fajr, and the people said takbir and he did not return, and they said "Subhan Allah" and he did not return, it is not permissible for them to follow him. Rather, they should remain. If they wish, they can wait; they may perform the final tashahhud and say taslim for themselves, or they may wait for him and say taslim with him. Then they should inform him that it was an extra rak'ah. It is not permissible for them to follow him while they know it is extra.
As for if he stood up from the first tashahhud and remained standing, and they said "Subhan Allah" and he did not return, there is no harm on him, no harm on him. But he must perform sujud al-sahw; sujud al-sahw compensates for his leaving the first tashahhud. And if he remained standing, it is disliked for him to return, even if they said "Subhan Allah." Yes.