If you set attrib accept-charset for Zend_Form,

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fieldset> will render with accept-charset too, which produces invalid XHTML. Solution is easy, just add 'accept-charset' into $stripAttribs array in Zend/Form/Decorator/Fieldset.php

Index: Fieldset.php
===================================================================
--- Fieldset.php    (revision 19215)
+++ Fieldset.php    (working copy)
@@ -39,20 +39,21 @@
     /**
      * Attribs that should be removed prior to rendering
      * @var array
      */
     public $stripAttribs = array(
         'action',
         'enctype',
         'helper',
         'method',
         'name',
+        'accept-charset',
     );
 
     /**
      * Fieldset legend
      * @var string
      */
     protected $_legend;
 
     /**
      * Default placement: surround content