Unexpected false return value from android.hardware.SensorManager.registerListener in Android 4.3

Question

Used LG Nexus 4, Android 4.3

The return value is sometimes false and I don't understand why. Documentation says: "true if the sensor is supported and successfully enabled."

What is strange is that no examples I've seen is testing return value from SensorManager.registerListener.

Strange is it also that if I ignore that a false value is returned then everything works as expected!

Documentation: http://developer.android.com/reference/android/hardware/SensorManager.html

android.hardware.SensorManager, android.hardware.SystemSensorManager

My code:

SensorManager sensorMgr = (SensorManager)_context.getSystemService(Context.SENSOR_SERVICE);
if (sensorMgr == null) {
    Log.w(TAG, "200410::Sensors not supported");
    return false;
}

Sensor sensor = sensorMgr.getDefaultSensor(Sensor.TYPE_PROXIMITY);
result = sensorMgr.registerListener(this, sensor, SensorManager.SENSOR_DELAY_NORMAL);
if( result == false) {
    // Normally something should be done here
    // since the false return value indicated that registration failed.
    // But I found it's better doing nothing since the registration seams to be ok
}
return result;

The strange false return value did not happened before Android 4.3

So, I everything is ok if the result value is not used like in all examples. Maybe I should be satisfied by that, but, I have 3 questions:

1. Why is this return value never tested in examples?
2. Why is return value false in Android 4.3?
3. Why is it working even if the return value is false?

I understand these questions are difficult to answer but would be very happy if I get info that someone else have the same problem.

I got the same behavior with both Sensor.TYPE_ACCELEROMETER and Sensor.TYPE_PROXIMITY