Currently, Zend_Controller_Dispatcher_Standard does not allow controllers in the default module to be namespaced. This can cause an issue if setting the default module to a name other than 'default' in order to have an existing module be the default. A simple change to loadClass() would fix this. The new method would look like this:

public function loadClass($className)
{
    $dispatchDir = $this->getDispatchDirectory();

    $loadFile    = $dispatchDir . DIRECTORY_SEPARATOR . $this->classToFilename($className);
    $dir         = dirname($loadFile);
    $file        = basename($loadFile);

    try {
        Zend_Loader::loadFile($file, $dir, true);
    } catch (Zend_Exception $e) {
        require_once 'Zend/Controller/Dispatcher/Exception.php';
        throw new Zend_Controller_Dispatcher_Exception('Cannot load controller class "' . $className . '" from file "' . $file . '" in directory "' . $dir . '"');
    }

    $final = $this->formatModuleName($this->_curModule) . '_' . $className;

    if (!class_exists($final)) {
        if ((($this->_curModule == $this->_defaultModule) 
                && !class_exists($className))
            || ($this->_curModule != $this->_defaultModule))
        {
            require_once 'Zend/Controller/Dispatcher/Exception.php';
            throw new Zend_Controller_Dispatcher_Exception('Invalid controller class ("' . $className . '")');
        }
        $final = $className;
    }

    return $final;
}