Apostolic Administrators are appointed when the bishop is unable to carry on in the diocese. The person appointed as Apostolic Administrator is not supposed to have any other diocese under him. For many years, following the ouster of the Portuguese, when Archbishop of Goa and Patriarch of East Indies was in Portugal, Raul Gonsalves was the Apostolic Administrator.
Since Benedict XVI became pope many bishops who are transferred to other dioceses or promoted as archbishops are appointed as Apostolic Administrators where they were bishops. This is not a good sign. Thomas Dabre after becoming Bishop of Poona is the Apostolic Administrator of Vasai.
When a bishop is transferred or promoted a new bishop must be appointed or diocesan consultors or curia must elect an administrator or Vicar Capitular. A bishop being Apostolic Administrator of another diocese reminds me of Pre-Reformation days when many bishops had two or more dioceses under them. In some cases those appointed as bishops were not consecrated for years.
The practice of one bishop having two or more dioceses under him must stop.