A vacancy on the commission shall be filled by a majority vote of the remaining members of the commission at the earliest practicable date after the vacancy occurs and the person appointed shall serve until the next regular commission election. If the vacancy is in the office of mayor, the commission shall appoint a mayor from its own members if less than one year remains in the term of the mayor; however, if one year or more remains in the term of the mayor, the remaining members of the commission may appoint a mayor from its own members or call a special election to be held on an authorized uniform election date to fill such vacancy. The commission shall not appoint more than one commissioner in any twelve month period, and in case a vacancy has been filled by the commission within twelve months prior to the subsequent vacancy, or if more than one vacancy occurs at the same time or before a prior vacancy has been filled, the commission shall order an election to be held on the next uniform election date provided by the Texas Election Code following the date the last vacancy occurred for the purpose of electing the successor or successors to the offices vacated. However, should a vacancy occur in the office of mayor and that office is filled as above provided, the vacancy in the office of commissioner thereby created shall not be counted when considering whether two (2) or more vacancies should be filled by election.