Help with Drag/Drop

Question

   private void Form1_Load(object sender, EventArgs e)
        {

            listBox1.DragDrop += new DragEventHandler(listBox1_DragDrop);

        }

  private void listBox1_DragDrop(object sender, DragEventArgs e)
        {
            string[] FileList = (string[])e.Data.GetData(DataFormats.FileDrop, false);
                      MessageBox.Show(FileList[0]);

        }

How come two messageboxes are shown when I drag a file in?