Updates of the Registration Reply received from the Home Agent at the Foreign Agent doesn’t invalidate the authentication data supplied by the Home Agent since the challenge extension is added after Mobile-Home Authentication extension. Hence the threat mentioned in section 12 (Security considerations) is not applicable.
Hence, it is recommended to remove second paragraph from section 12 (Whenever a Foreign Agent updates a field of the Registration Reply. This might happen when, in fact, a Registration Reply showing acceptance of the registration might soon be received by the mobile node).