wp_query orderby random not working

Can’t for the life of me get the orderby to be random in this wp_query. ‘rand’ not working at all.

Can anyone see why this code is still producing a list of posts in standard reverse chronological order instead of randomized mix?

function homex_top10_loop() {
	$args = array(
		'posts_per_page' => 10,
		'post_type' => 'post',
		'cat' => 4,
		'orderby' => 'rand'
	);
	//print_r($args);
	global $wp_query;
	$wp_query = new WP_Query( $args );