The problem didn't occur until I upgraded the unit to the latest firmware. Nothing yet connected to the rs485 port. Just preformed a factory reboot, no change.
Definitely a software problem, looked at /etc/init.d/serial force_tx_led_off(), executed echo 1 > sys/class/gpio0/value and the TX LED turns off, also /etc/init.d/serial stop works as well.
Also setting the rs485 serial to "console" mode and the LED is OFF, setting it to any other mode including "off" and the TX Led comes ON.