Index: wp-includes/class-wp-xmlrpc-server.php
===================================================================
--- wp-includes/class-wp-xmlrpc-server.php	(revision 23294)
+++ wp-includes/class-wp-xmlrpc-server.php	(working copy)
@@ -33,6 +33,9 @@
 	 * @return wp_xmlrpc_server
 	 */
 	function __construct() {
+		if ( ! WP_DEBUG ) {
+			set_error_handler( array( $this, 'handle_nonfatal_errors' ), E_WARNING | E_NOTICE | E_USER_WARNING | E_USER_NOTICE | E_STRICT | E_RECOVERABLE_ERROR | E_DEPRECATED | E_USER_DEPRECATED );
+		}
 		$this->methods = array(
 			// WordPress API
 			'wp.getUsersBlogs'		=> 'this:wp_getUsersBlogs',
@@ -5496,4 +5499,9 @@
 
 		return $pingbacks;
 	}
+	// handler ( int $errno , string $errstr [, string $errfile [, int $errline [, array $errcontext ]]] )
+	function handle_nonfatal_errors( $errno, $errstr, $errfile = nil, $errline = nil, $errcontext = nil ){
+		// Swallow non-fatal errors to prevent invalid XML
+		return true;
+	}
 }