Google has made some changes and modifications to its Webmaster Tools verification system related to management of website verifications.
Webmasters can now see who the verified users on their sites are and now the verification method they used to achieve that status. That's useful information to know when you're managing sites within Webmaster Tools that were once under the control of another individual or agency.
Google is also now requiring that that the verification method be removed from a site before unverifying an owner within Webmaster Tools. If the verification (for example a meta tag or an HTML file) then there will be an error message shown. It's easy enough really to remove meta tags and HTML files that were once used for site verification, but this change likely the result of the delay in updating DNS records (a common problem).
Finally, Google also modified the CNAME verification string, making it shorter in order to support more DNS providers. Google's long CNAME was causing some problems for some users who were not able to use the verification method because some DNS systems limit the number of characters than can be used in DNS records.