Zend_Validate_File_Count fails if you set a new file destination after isValid is called, and then call isValid again.

An example will better illustrate:

define('UPLOADS_PATH', '/path/to/uploads');

class Bug_Form_FileCountValidator {
    public function init() {
        $this->addElement('file', 'uploadElement', array(
            'label'         => 'Label text',
            'valueDisabled' => true,
            'validators'    => array(
                array('Count', true, array('max' => 1))
            )
        ));
        // ...
    }
}

$form = new Bug_Form_FileCountValidator();
$form->uploadElement->setDestination(UPLOADS_PATH);

if ($form->isValid($_POST)) {                       // A

    // set a new destination
    $form->uploadElement->setDestination(UPLOAD_PATH . '/newpath');

    $uploadElement->receive();                      // B
}

• The validation error message we get is: "Too many files, maximum '1' are allowed but '2' are given"
• isValid is called twice on: A & B.

A quick look at Zend_Validate_File_Count and you can see that by setting a new destination after isValid is called, it causes the file count validator to add another file reference to its count when isValid is called again with a new destination. However, two files don't actually exist, we have simply changed the destination of the file that the file count validator already knows about.

I hope that makes sense?