bbPress.org

Sorry, I was substituting pseudo-variable names in there: $site_title is the site title from the admin (“bbPress Support Forums” here) and the $topic_title is the topic title (this topic has “All RSS Feeds Broken?”). So, here, the RSS description is

bbPress Support Forums » Topic: All RSS Feeds Broken?

.......................^

and in a 1.0.1 installation it is

bbPress Support Forums Topic: All RSS Feeds Broken?

There is no raquo in the 1.0.1 installation, and the feed validator is complaining about that one character.