The SSL certificate for bugzilla isn't signed by a recognized CA. A real certificate is fairly cheap, and worth it, since there is no way for a user to be sure that someone isn't spoofing bugs.gentoo.org otherwise. People trust gentoo and bugs.gentoo.org and a malicious hacker could spoof bugs.gentoo.org and put in a "solution" to a bug which has a URL for a "bug fix" which actually points to an exploit. One can never be too paranoid.
*** This bug has been marked as a duplicate of 108944 ***