Comment 6 for bug 504976

"The TCP/IP port number for connecting to the slave" - its mean slave sql port number
"to be reported to the master during slave registration" - when slave server connect to master, master server set port number in show slave hosts to value of report-port of slave server.

Thats why there is notice - "Set this only if the slave is listening on a nondefault port".

Also --report-port=slave_port_num (http://dev.mysql.com/doc/refman/5.0/en/replication-options-slave.html#option_mysqld_report-port)

slave_port_num - i think its really slave sql port number, but not master sql port.