Index: wp-includes/IXR/class-IXR-introspectionserver.php
===================================================================
--- wp-includes/IXR/class-IXR-introspectionserver.php	(revision 56283)
+++ wp-includes/IXR/class-IXR-introspectionserver.php	(working copy)
@@ -73,7 +73,6 @@
         if (!$this->hasMethod($methodname)) {
             return new IXR_Error(-32601, 'server error. requested method "'.$this->message->methodName.'" not specified.');
         }
-        $method = $this->callbacks[$methodname];
         $signature = $this->signatures[$methodname];
         $returnType = array_shift($signature);