Zend_Form::_sort() may remove items from the internal _order, causing eg. some form elements to not be rendered.

This bug may present itself when both ordered and unordered items are used.

Reproduction

This example shows two bugs (Element overwrites DisplayGroup, and vice versa).

<?php

require "Zend/Form.php";

class TestForm extends Zend_Form
{
    public function init()
    {
        $this->addElement('text', 'alpha');
        $this->addDisplayGroup(array('alpha'), 'group-alpha');
        $this->getDisplayGroup('group-alpha')->setOrder(0);
        
        $this->addElement('text', 'beta');
        
        var_dump($this->_order);

        $this->_sort();
        
        var_dump($this->_order);



        $this->clearElements()
             ->clearDisplayGroups();

        $this->addElement('text', 'alpha');

        $this->addElement('text', 'beta');
        $this->addDisplayGroup(array('beta'), 'group-beta');
        $this->getDisplayGroup('group-beta')->setOrder(0);

        var_dump($this->_order);

        $this->_sort();

        var_dump($this->_order);
    }
}

new TestForm();

Output

array(2) {
  ["group-alpha"]=>
  NULL
  ["beta"]=>
  NULL
}
array(1) {
  ["beta"]=>
  int(0)
}
array(2) {
  ["alpha"]=>
  NULL
  ["group-beta"]=>
  NULL
}
array(1) {
  ["group-beta"]=>
  int(0)
}