I have just changed /etc/xinetd.d/ftp_psa to something like:
service ftp
{
disable = no
flags = REUSE
socket_type = stream
wait = no
user = root
server = /usr/sbin/proftpd
log_on_success += DURATION USERID
log_on_failure += USERID
nice = 10
bind = [IP to bind to]
}
And binding works fine after that.