Sec. 8. The several independent school districts and common school districts in such county shall continue to have authority to levy, assess, and collect the maintenance taxes theretofore authorized by the property taxpayers in said respective districts. This law shall not affect the right and duty of said respective school districts to levy, assess, and collect taxes within their respective districts for the payment of principal and interest on bonded indebtedness of such districts. The respective districts shall continue to levy, assess, and collect taxes sufficient to pay principal of and interest on their bonds. Provided, however, that nothing in this Act shall prevent the proper authorities from collecting and enforcing, for the benefit of the respective districts, any maintenance taxes levied before this law becomes effective.