Vacancies occurring for any reason other than the expiration of the term shall be filled by appointment for the unexpired portion of the term except if, on June 10, 1959, the unexpired portion of a term is for more than four years the vacancy shall be filled for a period of time that will obtain the maximum staggered terms, but shall not exceed four years. Vacancies shall be filled from the same commissioner district as that of the vacating member.