Index: branches/RC/core/kernel/utility/multibyte.php
===================================================================
diff -u -r10098 -r10123
--- branches/RC/core/kernel/utility/multibyte.php	(.../multibyte.php)	(revision 10098)
+++ branches/RC/core/kernel/utility/multibyte.php	(.../multibyte.php)	(revision 10123)
@@ -9,7 +9,7 @@
 
 		function mb_substr ($str, $start, $length = null, $encoding = null)
 		{
-			return substr($str, $start, $length);
+			return isset($length) ? substr($str, $start, $length) : substr($str, $start);
 		}
 
 		function mb_substr_count ($haystack, $needle, $encoding = null)
@@ -34,12 +34,12 @@
 
 		function mb_strrpos ($haystack, $needle, $offset = null, $encoding = null)
 		{
-			return strrpos($haystack, $needle, $offset);
+			return isset($offset) ? strrpos($haystack, $needle, $offset) : strrpos($haystack, $needle);
 		}
 
 		function mb_strpos ($haystack, $needle, $offset = null, $encoding = null)
 		{
-			return strpos($haystack, $needle, $offset);
+			return isset($offset) ? strpos($haystack, $needle, $offset) : strpos($haystack, $needle);
 		}
 
 		function mb_strlen ($str, $encoding = null)