301 is Redirecting to ServerAlias, not ServerName value

I'm seeing a behavior that I can't explain when someone types in a URL
without a trailing slash. It's redirecting to my first ServerAlias,
not my ServerName.

It was my understanding that a 301 should redirect to the ServerName,
not the ServerAlias. Am I incorrect?

>From my VirtualHost configuration:

ServerName www2.foo.com
ServerAlias www2-origin.foo.com rackspace.foo.com origin-
rackspace.foo.com

Thanks in advance!