Android AlertDialog leaks memory when show & dismiss multiple times?

I have a simple Activity with only one button to popup a simple dialog. Code is:

1. MainActivity.java

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    public void showDialogBlank(View dumbView) {
        AlertDialog.Builder dlgBuilder = new AlertDialog.Builder(this);
        dlgBuilder.setTitle("TEST-TITLE")
                .create()
                .show();
    }
}

2. activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <Button
        android:id="@+id/btnShowDialogBlank"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:onClick="showDialogBlank"
        android:text="btn-blank" />

</LinearLayout>

After I click the button & empty area multiple times, the memory is like:

Mainly, the Native memory grows by ~3.6MB, which cannot be GC... Why is that?

from Android AlertDialog leaks memory when show & dismiss multiple times?