Whenever part of a county has been transferred to another county, or a new county has been created out of an existing county, as provided by law, all civil, criminal, probate and other causes pending in the district and county courts of the original county, shall be transferred to the county as would be proper venue for such action or proceeding had the same been commenced after attaching said part of a county to an existing county, or creating said new county; provided, that the provisions of this section shall not apply to counties in which there is at present pending a court action to determine the legality of the transfer or transferring of any territory from one county to another county, or the creation of a new county, until the matter has been finally determined by the courts.