civicrm_membership_contact_get() does not respect 'is_test'

This code doesn't work. Test memberships are still returned.

require_once('api/v2/Membership.php');
$params = array(
'contact_id' => $contactID,
'is_test' => 0, //using 'member_is_test' doesn't work either
);
$allMemberships = civicrm_membership_contact_get($params);

I'd suggest that the default behavior of the function should be to exclude test membership; this would be consistent with the UI behavior. i.e., a developer would have to explicity supply a param if test memberships are desired.