Demo-code of a potential bug in ArduinoSTL

arduino_stl_printf_blocking.ino

#include <ArduinoSTL.h>

void setup() {
  Serial.begin(9600);
  pinMode(13, OUTPUT);
}

bool led_on = false;

void loop() {
  printf("running... ");
  digitalWrite(13, led_on = !led_on ? HIGH : LOW);
  delay(500);
}

serial_println_blocking.ino

void setup() {
  Serial.begin(9600);
  pinMode(13, OUTPUT);
}

bool led_on = false;

void loop() {
  Serial.println("running... ");
  digitalWrite(13, led_on = !led_on ? HIGH : LOW);
  delay(500);
}