SharePoint 2010 Managed Metadata Columns and Metadata Navigation Settings

Ok, here's another one I don't get. I created a new Team Site. I added a few test documents to the Shared Documents document library and tagged a few of the documents with some managed keywords:

I go into the library settings to verify that the Managed Keywords column is of type 'Managed Metadata':

I want to use the Managed Keywords column to drive metadata navigation. I go into the metadata navigation settings for the library:

The description for the navigation hierarchies clearly states that a column of type Managed Metadata field can be used for the navigation hierarchies. Yet I don't see my Managed Keywords column in the list of Avaiable Hierarchy Fields. So, of course, it doesn't show up in my navigation tree:

I'm not sure if this is a bug, if the description in the metadata navigation settings is incorrect, or if there's some configuration setting I'm missing. But it sure would be nice if that worked. That's going to help the users a heck of a lot if it works the way I think it's supposed to.