Render children of active branch with Zend Navigation view helper

What I am asking is similar to this issue, which is still unresolved.

I'm trying to create a good submenu solution, but I can't seem to get Zend_View_Helper_Navigation_Menu to work with me.

Here is my XML navigation config:

<configdata>
    <nav>
        <index>
            <label>Index</label>
            <uri>/</uri>
            <pages>

                <home>
                    <label>home</label>
                    <uri>/</uri>
                </home>

                <about>
                    <label>about</label>
                    <uri>/about</uri>
                </about>

                <works>
                    <label>works</label>
                    <uri>/works</uri>
                    <pages>
                        <music>
                            <label>music</label>
                            <uri>/works/music</uri>
                        </music>
                    </pages>
                </works>
                <posts>
                    <label>posts</label>
                    <uri>/posts</uri>
                </posts>                
                <admin>
                    <label>admin</label>
                    <uri>/admin</uri>
                    <pages>
                        <login>
                            <label>log in</label>
                            <uri>/admin/login</uri>
                        </login>
                        <settings>
                            <label>settings</label>
                            <uri>/admin/settings</uri>
                        </settings>
                        <register>
                            <label>register</label>
                            <uri>/admin/register</uri>
                        </register>
                        <logout>
                            <label>log out</label>
                            <uri>/admin/logout</uri>
                        </logout>
                    </pages>
                </admin>

            </pages>
        </index>
    </nav>
</configdata>

And here is the relevant code in my layout:

echo $this->navigation()->menu()->renderMenu(
    null, 
    array(
        'minDepth' => 2, 
        'maxDepth' => 2, 
        'onlyActiveBranch' => true
    )
);

When I navigate to 'admin', I don't see the submenu. If I change the minDepth to 1 I can see that that menu and its children are 'active' in the source. Why are they not being rendered when the minDepth is set to 2?

I did a workaround for this, but I have to copy/paste it into every controller for it to work (because I need the request object in order to do it):

    $pages = $this->view->navigation()->current()->getPages();
    foreach ($pages as $page) {
        $this->_setChildrenInvisible($page);
    }

the _setChildrenInvisible() function:

private function _setChildrenInvisible(Zend_Navigation_Container $container) {
    foreach ($container as $child) {
        if ($child->hasChildren()) {
            $this->_setChildrenInvisible($child);
        }
        $child->setVisible(false);
    }
}

Im just trying to get admin's children to render in the submenu. Does anyone know how to fix this?

In the layout, in the renderMenu method, the renderParents attribute should be set to false

echo $this->navigation()->menu()->renderMenu(
    null, 
    array(
        'minDepth' => 2, 
        'maxDepth' => 2, 
        'onlyActiveBranch' => true, 
        'renderParents' => false
    )
);