We have just released and fixed an incompatibility bug that was affecting users of v3.1.4 that were running their Wordpress on platforms using Automattic's Advanced Post Cache. This includes anyone running their site on Wordpress.com, whose sites use this caching mechanism even though the plugin doesn't appear in the WP Plugins area; Advanced Post Cache seems just built-in to the platform.
The way this incompatibility presented was that the
http://mysite.com/properties page [or whatever you set the Showcase IDX url to] would not show the property search application; instead it would typically just show the home page content.
Showcase IDX Wordpress Plugin v3.1.5 fixes this incompatibility with Advanced Post Cache. Simply update your plugin (which is now typically automatic thanks to recent Wordpress core update) and your site should be back to fully-functional immediately!