Masbooq and Laahiq

Joining a masbooq in Salaah

Q: I am a follower of the Shaafi'i mazhab. In our musjid, which is mainly Shaafi'i the Somalian brothers will join a masbooq who has missed a few raka'ats and they will then follow the masbooq as if he is the Imaam.

1. Is this correct? If yes how should it be done.

2. What should you do if you are the masbooq and someone taps your shoulder or just joins your Salaah to follow you? Your input in this regard is greatly appreciated.