pwm test 3- bug

// DRIVE_BACKWARD MAKES BOTH MOTORS GO BACKWARD, BUT DRIVE FORWARD MAKES ONLY 1 MOTOR (THE LEFT) GO FORWARD
void loop() {
  analogWrite(enable_pin_left, 255);
  analogWrite(enable_pin_right, 255);
  drive_backward();
  delay(1000);
  drive_forward();
  delay(1000);
}

// DRIVE_FORWARD MAKES BOTH MOTORS GO FORWARD, BUT DRIVE BACKWARD MAKES ONLY 1 MOTOR (THE RIGHT) FOR BACKWARD
void loop() {
  analogWrite(enable_pin_left, 255);
  analogWrite(enable_pin_right, 255);
  drive_forward();
  delay(1000);
  drive_backward();
  delay(1000);
}
// hmm, wonder why this is? anyone know?