In the event that it appears to the Board on reasonable grounds that an applicant or witness has not been truthful, or that a mistake has been made, and such circumstances bear on facts which are essential in the granting of the relief sought by the applicant and were relied upon by the Board taking action, then, upon discovery of such misrepresentation, fraud or mistake, the Board may rehear the matter, either on application of an interested party or on its own motion when unusual circumstances so require in the interests of justice. In such event, the Board may, upon notice directed to the applicant and all other interested parties, require the applicant to appear before it for the purpose of explaining the testimony previously given at the hearing. At such subsequent hearing, it may be determined whether or not the testimony as given at the original hearing was, in fact, false or mistaken. Mistake or fraud in proceedings, left uncured, shall constitute grounds for a rescission.