The SCLogin module will generate the logout link based on whatever scheme the current page is in. That's standard practice for Joomla as it will make relative links to URLs, which mean the scheme (http or https) and domain are unchanged from whatever page is currently being used.
My guess is that if you navigate to a non-https page and logout from there, you'll be redirected to the non-secure home page.
With that said, why do you really want to deny SSL on the home page? In general, more security is better and can make your visitors feel more comfortable. Just a suggestion, but we'd recommend not trying to force non-SSL. If users want to load a page over SSL (or are inadvertently redirected to it), let them use it that way.
I hope that helps,
Alex
Logout redirection url when SSL enabled
