Index: src/wp-includes/functions.php
===================================================================
--- src/wp-includes/functions.php	(revision 27218)
+++ src/wp-includes/functions.php	(working copy)
@@ -252,7 +252,13 @@
 	$data = trim( $data );
  	if ( 'N;' == $data )
 		return true;
+
+	mbstring_binary_safe_encoding();
+
 	$length = strlen( $data );
+
+	reset_mbstring_encoding();
+
 	if ( $length < 4 )
 		return false;
 	if ( ':' !== $data[1] )