I have the same problem. I looked in the code for about 5 mins and saw what I think is an error in the template file "profilebox.php". Looking at the "class.fireboard.php" file:
//Community Builder
if ($fbConfig['cb_profile'] || $fbConfig['fb_profile'] == "cb"

{
$database->setQuery("SELECT id FROM #__menu WHERE link = 'index.php?option=com_comprofiler' AND published=1"

;
$CB_Itemid = $database->loadResult();
define("FB_CB_ITEMID", (int)$CB_Itemid);
define("FB_CB_ITEMID_SUFFIX", "&Itemid=" . FB_CB_ITEMID);
}
The FB_CB_ITEMID_SUFFIX is referenced in the template file "profilebox.php":
$registerlink = sefRelToAbs('index.php?option=com_comprofiler&task=registers'.FB_CB_ITEMID_SUFFIX);
The logic in the code seems flawed because it's assuming that every Fireboard/CommBuilder integrator should have at least one published menu item open to the public corresponding to their communitybuilder "register" page.
For most of us, I would think, this would not be true. In fact, the only menu item I have for "com_profiler" is an item for the user to edit their profile, which only a registered user can do (which makes the point of using this link as a link to sign-up fruitless and causes the bug for me).
Anyhow, to "fix" this, I took out the appending of that suffix in this line and the "forgot password" one:
$registerlink = sefRelToAbs('index.php?option=com_comprofiler&task=registers'

;
$lostpasslink = sefRelToAbs('index.php?option=com_comprofiler&task=lostPassword'

;
Things seem to work for me this way. Perhaps this is a temporary fix. I suppose since this is in a template file people can fix this themselves in their respective templates. Maybe that's why the "login" link goes to the homepage, people can set this value themselves (I just removed it).
Hope this helps.
Robert
www.thomaspittman.com