"tax_query" parameter not working with WP_Query

I have a custom post type called ‘episode’. Attached to ‘episode’ I have a custom taxonomy called ‘video_type’ that contains two terms: “bonus-footage” and “episode”; “episode” contains two child terms “season-1” and “season-2” (other seasons will be added in the future). I want to grab only the most recent post of the ‘episode’ type but not include any posts from the ‘bonus-footage’ term. Below is the code I’m using for this:

<?php
$some_args = array(
	'tax_query' => array(
            'taxonomy' => 'video_type',
            'terms' => 'bonus-footage',
            'field' => 'slug',
	    'include_children' => true,
            'operator' => 'NOT IN'
	),
	'posts_per_page' => 1,
	'post_type' => 'episode',
);

$s = new WP_Query( $some_args );

if ( $s->have_posts() ) : $s->the_post();
	// Do something with this post.
endif;
?>

The query works as expected if a post in one of the ‘season’ terms is the newest, but if a post in “bonus-footage” is the newest, then it’s loading that one. In other words my “tax_query” parameters appear to have no affect on the query. Am I not formatting the “tax_query” properly or am I missing something else?

I’ve also tried setting “tax_query” as below:

'tax_query' => array(
            'taxonomy' => 'video_type',
            'terms' => 'episode',
            'field' => 'slug',
	    'include_children' => true,
            'operator' => 'IN'
	),

but I’m still getting the same result.