Is the Maghrib prayer valid for someone who prayed with a late congregation with the intention of catching up with friends for the Isha prayer, and separated from the Imam in the second rak'ah after completing the Maghrib prayer?

This issue discusses whether a traveler can be led in the 'Isha prayer by someone praying Maghrib. It is preferable to avoid this. If a traveler prays behind someone praying Maghrib, he is obligated to complete the prayer because he is being led by someone who is completing their prayer. Therefore, he must repeat the prayer in full.