Index: /branches/Ver2.4/xpressme_integration_kit/include/oninstall.php
===================================================================
--- /branches/Ver2.4/xpressme_integration_kit/include/oninstall.php	(revision 796)
+++ /branches/Ver2.4/xpressme_integration_kit/include/oninstall.php	(revision 797)
@@ -300,13 +300,8 @@
 if( ! function_exists( 'sanitize_user_multibyte' ) ) :
 function sanitize_user_multibyte($username, $raw_username, $strict){
-	if ($username == "" && $strict){
-		if ($raw_username == ""){
-			return $username;
-		} else{
-			return sanitize_user($raw_username, false);
-		}
-	} else {
-		return $username;
-	}
+	if ($raw_username !== "" && $username !== $raw_username){
+		return $raw_username;
+	}
+	return $username;
 }
 endif;
Index: /branches/Ver2.4/xpressme_integration_kit/wp-content/plugins/xpressme/xpressme.php
===================================================================
--- /branches/Ver2.4/xpressme_integration_kit/wp-content/plugins/xpressme/xpressme.php	(revision 796)
+++ /branches/Ver2.4/xpressme_integration_kit/wp-content/plugins/xpressme/xpressme.php	(revision 797)
@@ -84,18 +84,15 @@
 
 // enable multibyte username
-if( ! function_exists( 'sanitize_user_multibyte' ) ){
-	function sanitize_user_multibyte($username, $raw_username, $strict){
-		if ($username == "" && $strict){
-			if ($raw_username == ""){
-				return $username;
-			} else{
-				return sanitize_user($raw_username, false);
-			}
-		} else {
-			return $username;
+if( ! function_exists( 'sanitize_user_multibyte_at_update' ) ){
+	function sanitize_user_multibyte_at_update($username, $raw_username, $strict){
+		if (isset($_POST['action']) && $_POST['action'] == 'update'){
+			if ($raw_username !== "" && $username !== $raw_username){
+				return $raw_username;
+			} 
 		}
+		return $username;
 	}
 }
-add_filter('sanitize_user', "sanitize_user_multibyte" ,10,3);
+add_filter('sanitize_user', "sanitize_user_multibyte_at_update" ,10,3);
 
 add_action('admin_menu', 'my_plugin_menu');