BBN
Fractal Fanatic
At first glance, you'd think so. But look closely at the tip connection of the stereo jack. You'll see that the wire from the mono jack goes to a different side of the stereo jack. When there's nothing plugged into the stereo jack, the tip connection passes through from one side of the stereo jack to the other, and both speakers are in parallel. But when there's a plug in the stereo jack, that connection is broken, and the tip of the plug in the stereo jack becomes the new source for the other speaker.
With this type of jack, you can actually see the connection being made and broken as the plug goes in and out of the jack.
And there it is......thanks for the explanation Rex!