wp-term-query-test.php

<?php 

// didn't work
	$term_args = array(
		'taxonomy' => 'issuem_issue', // passed as a string
		'meta_query'	=> array(
			array(
				'key'	=> 'old_id',
				'value' => 123,
				'compare' => '='
			)
		)
	);
	
$term_query = new WP_Term_Query( $term_args );


// did work
	$term_args = array(
		'taxonomy' => array( 'issuem_issue' ), // passed as an array 
		'meta_query'	=> array(
			array(
				'key'	=> 'old_id',
				'value' => 123,
				'compare' => '='
			)
		)
	);
	
$term_query = new WP_Term_Query( $term_args );