Question:  If the sajdah-sahw becomes (correcting a mistake in Salah) wajib upon the Imam, do the Musalli including masbuk has to do the Sajdah-sahw with Imam? 

Answer: According to the rule of following Imam per say in Salah, all musalli including masbuk has to do Sajdah-sahw but should not do salam with Imam. If one does it without knowing or forgetfully then it’s ok otherwise it will render the salah invalid for Musallis and Masbuk.

References: [1] Ad durr-ul-mukhtar vol-2:82 [2] Fathul Qadeer vol-1:44 [3] Hidaya vol-1:158 [4] Al-Bahrur Raiq vol-2/100