Something on your site is definitely altering the URLs for redirection. On every page that I go to, the redirection is set properly with the correct Itemid for the current page. For example, on the JomSocial home page, the redirection looks (and should be):
/index.php?option=com_community&view=frontpage&Itemid=188
However, after logging out, the actual URL is:
/index.php?option=com_community&view=frontpage&Itemid=1
I'm not sure what's doing that, but you'll need to narrow it down.
The only other suggestion I can give you is to enable the "Logout of Joomla Only" setting. That will not log the user out of Facebook and will use the "Logout Redirection" setting of the SCLogin module, which may change the behavior. That shouldn't be necessary, but again, I'm not sure what's altering or redirecting to Itemid=1 always.
I hope that helps,
Alex