Stopping DialogResult.OK cascading through windows

I currently have an application (yes, it's an assignment, but this is just me cleaning up the app for better presentation) that opens a dialog window, which can open another window for confirmation of a deletion. Clicking cancel on this second dialog window cascades down to the first dialog window, and returns everything back to the main application window.

How can I prevent this from happening? What work arounds are there?

Code:

---

// example

private void ShowAppointmentWindow()
{
  ApptWindow newWindow1 = new ApptWindow();
  if(newWindow1.ShowDialog() == DialogResult.OK)
  {
    // do some stuff saving the appointment basically
  }
}

// then

private void ShowDeleteBox()
{
  if(MessageBox.Show("blah","Sure?", *etc etc*) == DialogResult.OK)
  {
    // do some stuff to delete
  }
}

---

Yes it's an assignment, but this aside, it's done, literally ready to print and burn to CD even without doing this bit (no marks for this anyway).