How to switch between normal and "full width" ASCII with Microsoft Pinyin IME?

Question

I've installed a couple of Input Method Editors (IMEs) while trying to learn some Chinese.

Clicking the shift key on its own normally changes between Chinese input and English / ASCII input.

But once in a while it will switch to ｆｕｌｌｗｉｄｔｈ　ｍｏｄｅ for seemingly no reason.

When this happens I can't seem to find a way to switch it back to normal width mode. I would prefer a way to do it from the keyboard, but a way to do it from the system tray would also be worth knowing:

Solution

Aha, I finally found the answer after posting here.

On a site for learning Chinese and Japanese called "Skritter" is a 2011 post from user "peanutbutter":

...
BUT if you happen to press Shift + space bar, you get that weird ugly spaced font we see above. Pressing shift + space makes it toggle back.
...

Now I can switch ｂａｃｋ　ａｎｄ　ｆｏｒｔｈ at will!