oid 2.5.6.7 NAME 'organizationalPerson' SUP person
may differs: [('title', 'x121Address', 'registeredAddress', 'destinationIndicator', 'preferredDeliveryMethod', 'telexNumber', 'teletexTerminalIdentifier', 'telephoneNumber', 'internationalISDNNumber', 'facsimileTelephoneNumber', 'street', 'postOfficeBox', 'postalCode', 'postalAddress', 'physicalDeliveryOfficeName', 'ou', 'st', 'l')] vs. [('title', 'x121Address', 'registeredAddress', 'destinationIndicator', 'preferredDeliveryMethod', 'telexNumber', 'teletexTerminalIdentifier')]

MAY ( title $ x121Address $ registeredAddress $
destinationIndicator $ preferredDeliveryMethod $
telexNumber $ teletexTerminalIdentifier $
telephoneNumber $ internationalISDNNumber $
facsimileTelephoneNumber $ street $ postOfficeBox $
postalCode $ postalAddress $ physicalDeliveryOfficeName $
ou $ st $ l )

person is defined as this:
MAY ( userPassword $
telephoneNumber $
seeAlso $ description )

When parsing the list of attrs in the child to see if the attr is already listed in the parent, once the parser hits the first one (in this case, telephoneNumber), it leaves out the rest. In this case, telephoneNumber and everything after that (internationalISDNNumber, etc.)