Meta Queries – should nesting work after WP 4.1?

I have a rather huge meta_query here and it hangs at execution: browser just won’t load the page, it goes on loading …

As far as I know this should work after WP 4.1 (I have it). Also tried updating to 4.2 to no avail.

Am I doing something terribly wrong here? Thanks for any info.

$meta_query = array(
    'relation' => 'AND',

    // IF $level GIVEN
    array(
        'relation' => 'OR',
        array(
            'key' => 'co_level',                 
            'value' => $level,                  
            'compare' => 'IN'   
        ),
        array(
            'relation' => 'AND',
            array(
                'key' => 'co_program2',
                'value' => $program_ids,
                'compare' => 'IN'
            ),
            array(
                'key' => 'co_level2',                 
                'value' => $level,                  
                'compare' => 'IN'   
            ),

        ),
        array(
            'relation' => 'AND',
            array(
                'key' => 'co_program3',
                'value' => $program_ids,
                'compare' => 'IN'
            ),
            array(
                'key' => 'co_level3',                 
                'value' => $level,                  
                'compare' => 'IN'   
            ),
        ),             

    ),

    // IF $year GIVEN
    array(
        'relation' => 'OR',
        array(
            'key' => 'co_year', 
            'value' => $year, 
            'compare' => 'IN'
        ),
        array(
            'relation' => 'AND',
            array(
                'key' => 'co_program2',
                'value' => $program_ids,
                'compare' => 'IN'
            ),
            array(
                'key' => 'co_year2', 
                'value' => $year, 
                'compare' => 'IN'
            ),
        ),  
        array(
            'relation' => 'AND',
            array(
                'key' => 'co_program3',
                'value' => $program_ids,
                'compare' => 'IN'
            ),
            array(
                'key' => 'co_year3', 
                'value' => $year, 
                'compare' => 'IN'
            ),
        ),
    ),  
);

$args = array( 
    'post_type' => 'course',
    'posts_per_page' => -1,             // get all posts

    'orderby' => array('meta_value_num'=>'ASC','menu_order'=>'ASC'),        // order by given meta value AND menu_order
    'meta_key' => $meta_key_orderby,
    'order' => 'ASC',

    'meta_query' => $meta_query,

);