XML : Control Description Doesn't Show

I'm working on a custom Ribbon UI for an Excel-based tool. I'm developing for Excel 2013. During testing I was asked if I could add descriptions to a few of the button controls. I knew I'd seen this in documentation before so I looked it up and found this:

That seemed easy enough, so I added a description to a few of the button controls, checked the XML syntax (I'm using Custom UI Editor for Microsoft Office), and saved the changes. When I opened the file I didn't see the descriptions on the buttons, so I checked the XML to ensure I had saved them. I had.

I tried using getDescription instead, but the callback isn't even triggered when the ribbon loads... So eventually I copied the XML from the description and pasted it into my ribbon. This is what it looks like on my ribbon:

Code from documentation:

  <button   id="button" label="Button" imageMso="HappyFace"       description="This is a verbose description that describes       the function of this control in detail." />    

Result on my ribbon:

Versus what the documentation says the above code will produce:

So where's the description?

Now I know the documentation was written for either Office 2007 or 2010, so I'm wondering if description and getDescription were deprecated for 2013, or if something else is going on here.

Does anyone know why the description isn't showing in Office 2013?