Purpose of RX and TX LEDs?

Hardware Arduino Zero
13

I attempted to write a very simple sketch to blink the three on-board LEDs on a Zero.

EXPECTED

Time L Tx Rx
0 sec
1 sec ON
2 sec
3 sec ON
4 sec
5 sec ON
6 sec
7 sec ON
8 sec
9 sec ON

ACTUAL

Time L Tx Rx
0 sec
1 sec ON
2 sec ON
3 sec ON ON
4 sec ON
5 sec ON ON
6 sec
7 sec ON
8 sec ON
9 sec ON ON

The problem with the actual results is that the L LED stays on when it shouldn't.

Can anyone figure out what’s happening here? Thanks.

Here is my code:

/*============================================ 
  Blink the three on-board LEDs in sequence
============================================*/

#include "Arduino.h"
#define LED_CNT  3    // number of on-board LEDs:

// define an array of the on-board LEDs:
int ledPin[] = {
  PIN_LED,            // labeled "L" on the board:
  PIN_LED3,           // labeled "TX" on the board:
  PIN_LED2            // labeled "RX" on the board:
};

int led = 0;

void setup() {
  // initialize each pin as an output:
  for (int i = 0; i < LED_CNT; i++)
    pinMode( ledPin[ i ], OUTPUT );
}

void loop() {
  // clear all LEDs:
  for (int i = 0; i < LED_CNT; i++)
    digitalWrite( ledPin[ led ], LOW  );

  // blink the selected LED:
  delay(1000);
  digitalWrite( ledPin[ led ], HIGH );
  delay(1000);

  // choose next LED:
  led += 1;
  if ( led >= LED_CNT ) led = 0;
}