Hi, just wanted to share that I am having this exact same problem:
The coming soon page will NOT turn off even though its disabled in every template copy under template styles. I want the normal joomla login page with logo using offline mode.
If I turn on maintenance mode with the template 'coming soon' feature turned off, it still shows the coming soon resources, but there is no login module any more. Even if I turn coming soon back on, I can't get back to having a login box. Definitely something very broken with this feature. I cleared all my caches, cleared my browser cache, checked everything, but no joy.
So I wanted to revert back to the default Joomla offline mode which you know, just works. But no, I can't!
Simple solution:
In the template folder, back up the offline.php file (which is what powers the under maintenance page) and then delete it. Back to the standard Joomla offline page. Tada!