StartCom SSL certificates not validating in Mountain Lion?

For whatever reason, it looks like Apple may not have included a StartCom SSL root certificate in Mountain Lion. When I visit a site with an SSL certificate signed by StartCom, Safari reports that the certificate is invalid.

The problem only appears to exist in Safari on a from-scratch install of Mountain Lion. Macs upgraded from a previous release of OS X are not affected, and the problem is not present in other browsers such as Mozilla Firefox on any release.

To rule out any weird issue specific to me, please would someone with a fresh OS X 10.8 install load the following:

https://www.startcom.org

and let me know if the browser displays an invalid certificate warning or not?

Many thanks.