On the free version default template, there is a call to an undefined $title reference and you'll get traces. So it looks like a little detailed overlooked.
After fixing this it works nicely.
I still give 4 stars cause I found through the documentation about the Joomla MVC feature that allowed me to fix the SIG default template within my own site template, without modifying the core plugin and still get updates.
It would have been nice to be able to customize the global messages but I also understand why they've been up into the language files.
Actual the MVC overrides for the plugin is not a standard Joomla "thing" for plugins. It's how JoomlaWorks implements MVC on most of its plugins so designers can easily change a plugin's HTML output with not too much fuss.
Regarding your issue, it would help if you could submit your issue on our forum and mention the PHP version your server is running or whether you had error reporting in the global configuration of Joomla set to maximum or not...