When running multisite with mapped domains, the plugin content loads from the unmapped domain. This can cause problems with cacheing. I modified the plugin as follows to change this behaviour:
//if ( !defined('WP_CONTENT_URL') ) {
define('SMW_PLUGINPATH',get_option('siteurl').'/wp-content/plugins/'.plugin_basename(dirname(__FILE__)).'/');
define('SMW_PLUGINDIR', ABSPATH.'/wp-content/plugins/'.plugin_basename(dirname(__FILE__)).'/');
/*} else {
define('SMW_PLUGINPATH',WP_CONTENT_URL.'/plugins/'.plugin_basename(dirname(__FILE__)).'/');
define('SMW_PLUGINDIR',WP_CONTENT_DIR.'/plugins/'.plugin_basename(dirname(__FILE__)).'/');
}*/