it is down to the templates_c folder.
This is where the templates are compiled (c) ready to display in the browser. When you make changes to the templates they are re-compiled in the templates_c folder.
This folder must have a chmod value of 777 to work correctly.
To clear the templates_c folder you would run
www.yoursite.com/xcartdir/cleanup.php . This would force x-xcart to re-compile the store with your changes