I've SCANed your subscriber list for the nike.com uses: those
were the only two and they appeared only once (unless concealed).
 
I suspect any one of the following:
 
1) the NIKE.COM SMTP RFC821 RCPT TO authentication system is broken
 
2) NIKE.COM SMTP doesn't understand multiple RFC821 RCPT TO:
   fields without mapping to RFC822 recipients
 
3) a bug in LISTSERV distribute (highly unlikely)
 
Pete Weiss at Penn State