WP get_categories甚至奇数增量选择器的问题

I have a small function in my WordPress theme which generates a list of menus depending on category id. I have also setup an even/odd identifier to add spacers in between, the last one is removed via jQuery (unless you can provide a way of doing this in PHP code).

Each menu shows the spacers accordingly apart from one random one?

function momentmag_tertiary_nav($cat_ID, $name = '') {

    $categories = get_categories( array('child_of' => $cat_ID, 'hide_empty' => false) );
    $siteurl = get_bloginfo('url');
    $i = count($categories);

    $catparent = get_categories( array('include' => $cat_ID, 'hide_empty' => false) );

    echo '<ul class="'.$name.'-drop">';

    foreach($categories as $category) {

        echo '<li><a href="'.$siteurl.'/'.$catparent[0]->slug.'/'.$category->slug.'" title="View Articles in: '.$catparent[0]->cat_name.' &rarr; '.$category->cat_name.'">'.$category->cat_name.'</a></li>';
        if ($i % 2 != 0) {                      
            echo '<li class="spacer"></li>';            
        }   

    }   

    echo '</ul>';   

}

Example of working menu:

Then this one randomly doesn't apply the spacers where as all the others do, there is 10 in total:

any ideas? this is really dodgy!