Upon the trial of an issue formed on an affidavit of illegality, the jury trying the case shall have power to assess such damages as may seem reasonable and just, not exceeding 25 percent of the principal debt, where it is made to appear that the illegality was interposed for delay only. Whenever an illegality is dismissed for insufficiency or informality or is withdrawn, plaintiff in execution may proceed as is provided in cases where claims are dismissed or withdrawn.