--- formatting.php	2013-06-03 11:27:18.751480979 +0300
+++ formatting.new.php	2013-06-03 11:31:58.011098003 +0300
@@ -1835,7 +1835,7 @@
 		}
 
 		// Test for invalid characters
-		if ( !preg_match('/^[a-z0-9-]+$/i', $sub ) ) {
+		if ( !preg_match('/^[\d|\p{Ll}]+$/u', $sub ) ) {
 			return apply_filters( 'is_email', false, $email, 'sub_invalid_chars' );
 		}
 	}