I-94 Form Expiration Date

My parents arrived USA on Dec 26, 2006 with a return ticket on June 25, 2007. However, the I-94 "Arrival/Departure Document" form they received was stamped with an expiration date of June 24, 2007, one day earlier than their planned return date. To change their return date, they have to pay extra change fees with the airline. They would not like to extend their stay to risk their next visa application, either. Do you have any similar experience or insight regarding this situation? If they leave on Dec 26, will it be regarded as a violation so that their next visit to the USA might be jeopardized? Thank you so much for your help in advance.