[Plugin: WordPress.com Stats] Stats for Multiple Domains

My blog is mirrored by a number of domains, including uttertosser.com and richardhmorris.com. When I visit richardhmorris.com, the stats smiley is shown at the bottom of the page, but when I visit uttertosser.com it’s not.

Why is this? Does it matter which one is the “master” domain name for the WordPress setup? Does it matter that uttertosser.com is the one listed as one of my blogs under the WordPress API login?