Order Warning

When I have an array as part of the main query orderby field I get the following warning:

Warning: Illegal offset type in isset or empty in C:\wamp\vhosts\wp-3.9\wp-includes\taxonomy.php on line 230
Call Stack
#	Time	Memory	Function	Location
1	0.0020	235608	{main}( )	..\index.php:0
2	0.0030	238712	require( 'C:\wamp\vhosts\wp-3.9\wp-blog-header.php' )	..\index.php:17
3	1.4610	42578080	wp( )	..\wp-blog-header.php:14
4	1.4610	42578376	WP->main( )	..\functions.php:873
5	1.4640	42653248	WP->query_posts( )	..\class-wp.php:611
6	1.4640	42653704	WP_Query->query( )	..\class-wp.php:540
7	1.4640	42659992	WP_Query->get_posts( )	..\query.php:3836
8	1.4680	42703672	apply_filters_ref_array( )	..\query.php:3249
9	1.4680	42704648	call_user_func_array:{C:\wamp\vhosts\wp-3.9\wp-includes\plugin.php:269} ( )	..\plugin.php:269
10	1.4680	42705792	CPT_ONOMIES_MANAGER->posts_clauses( )	..\plugin.php:269
11	1.4680	42705792	CPT_ONOMIES_MANAGER->is_registered_cpt_onomy( )	..\manager.php:343
12	1.4680	42705792	taxonomy_exists( )	..\manager.php:833

https://wordpress.org/plugins/cpt-onomies/