The other day we reported that Google Webmaster Sitemaps Tool Back With Old Data? where I said, there was in issue with the common words. The issue is most likely old data. Vanessa Fox replied to the forum thread at WebmasterWorld saying;
As Googlebot recrawls the site, you should see the common words table updated to reflect the new content.
I then found a Google Sitemaps blog post named Unexpected Common Words that gives a few reasons why you may find "unexpected common words" in the report.
(1) Googlebot hasn't crawled all pages on your site. (2) Your site has changed since we last crawled it. (3) Googlebot is unable to re-crawl modified pages. (4) Your site is not being crawled.
Continued forum discussion at WebmasterWorld.