I am not sure if I have the same issue. I recently re-built my site on Wordpress. It did not change domain names but I did move the site from a template site company to a Bluehost Wordpress implementation. Using Yoast's WordPress SEO plugin my XML sitemaps are also not showing up in Google Webmaster tools. I get the following error from Google:
We encountered an error while trying to access your Sitemap. Please ensure your Sitemap follows our guidelines and can be accessed at the location you provided and then resubmit.
General HTTP error: 404 not found
HTTP Error: 404
Going to http://creativecakesallison.com/page-sitemap.xml it looks like the Sitemaps are set up correctly. Any idea why Google can't see the Sitemaps?