WP_Query Memory problem only on Result-less Queries

I’m writing a plugin and the following query keeps exhausting my memory ONLY when the query should return no results:

(The two variables are totally fine numeric timestamps.)

$query_args = array(
		'post_type' => 'cets_event',
		'order' => 'ASC',
		'orderby' => 'meta_value_num',
		'meta_key' => '_ez_start_date',
		'meta_query' => array (
										array(
											'key' => '_ez_start_date',
											'value' => $ts_start_of_month,
											'compare' => '>',
										),
										array(
											'key' => '_ez_start_date',
											'value' => $ts_end_of_month,
											'compare' => '<',
										),
								)
	);

	$event_query = new WP_Query( $query_args );

As you can probably guess, it grabs all the events from a given month. It works just fine on any month that has any events created for it, but keeps running out of memory otherwise.

It _really_ shouldn’t be any kind of actual memory issue, as I have 128M available and have not run into a single memory issue before ever.

The memory runs out from /wp-includes/query.php on line 2941 (the call to get_posts)

Any ideas?