Hey there -
I've tested this in both 2.0-rc1 and 2.0-dev, I'm having the same problem in both.
I'm trying to set the root of the breadcrumb to an external URL. I've entered the URL as "http://www.blahblah.com/stuff" and instead of it going to the URL, it interprets it as a Drupal URL after chopping off the http://. So, it turns into "http://www.my.site/www.blahblah.com/stuff".
I read a post that says that external URLs should work, so I've categorized this as a bug report. Even though it might be a feature request. :)