If, during an inter partes proceeding involving an application under section 1 or 44 of the Act, facts are disclosed which appear to render the mark unregistrable, but such matter has not been tried under the pleadings as filed by the parties or as they might be deemed to be amended under Rule 15(b) of the Federal Rules of Civil Procedure to conform to the evidence, the Trademark Trial and Appeal Board, in lieu of determining the matter in the decision on the proceeding, may remand the application