DURING AN EXTREMELY HARD STOP AND SWERVE TO AVOID A VEHICLE PULLING OUT OF IT'S LANE, THE FRONT PASSENGER SEATBELT POPPED OUT OF ITS HARNESS AND THE PASENGER WAS PROPELLED IN TO THE DASH.THE SEATBELT WAS PROPERLY SECURED, AND AFTERWARDS WE WERE UNABLE OT DUPLICATE THE PROBLEM BY PULLING HARD ON THE SEATBELT.