title: SpeechSynthesizer.SpeakAsyncCancelAll() does not cancel
body: <p>I have a button on my form that is labeled Speak, when user clicks on it <code>synth.SpeakAsync(Textbox.text)</code> is fired, and the button changes its text to "Stop Speaking".</p>
  
  <p>However when a user clicks on stop speaking, thereby firing the <code>synth.speakAsyncCancelAll()</code> it doesn't cancel the speech mid text.</p>
  
  <p>HERE IS MY CODE:</p>
  
  <pre><code>Private Sub btnSpeak_Click(sender As System.Object, e As System.EventArgs) Handles btnSpeak.Click
      If RTextBox.Text = "" Then Exit Sub
  
      Dim synth As New SpeechSynthesizer
      synth.Rate = -2
  
      If btnSpeak.Text = "Stop Speaking" Then
          btnSpeak.Text = "Speak"
          synth.SpeakAsyncCancelAll()
  
      ElseIf btnSpeak.Text = "Speak" Then
          btnSpeak.Text = "Stop Speaking"
          synth.SpeakAsync(RTextBox.Text)
      End If
  </code></pre>