Hello Speak Example - Switching of voice name does not actually stop the "speaking"

Description:

Switching the voice name while the speaking is being played creates issue where you cannot click on pause or stop anymore. These buttons become active only after the text is read in is entirety. 
Steps to reproduce:

1. Open the Hello speak example
2. Click on "Speak"
3. Change the voice name while the speaking is going on.
4. The "Pause" and "Stop" buttons are now inactive.

Expected behavior:

The "speaking" should stopped when a new voice name is selected.
Observed behavior:

There is a bottom note indicating that the speaking as stopped, but it in fact continues and the "Pause" and "Stop" buttons are now inactive.

Special notes:

At the bottom of the screen there is a note saying that the "speech stopped" but this is actually not the case as you can still hear it.

The "Pause" and "Stop" buttons are active again after you start a new "speak".