Informal disposition may be made of any contested case by stipulation, agreed settlement, consent order or default. No stipulation or agreed settlement between the parties or their attorneys or representatives, with regard to any matter involved in any proceeding before the Board, shall be enforced unless it shall have been reduced to writing and signed by the parties or their authorized representatives and made a part of the record, or unless it shall have been dictated into the record by them during the course of a hearing or incorporated in an order bearing their written approval.