relation => 'AND' is not working.

Hi,

I'm having an issue getting relation => 'AND' to work.

My code is:

'include' => array (
  	'relation' => 'AND',
 	'slug' => 'prototype-phase',
	 'phases' => 'setup',
),

Phases is a custom taxonomy I have created. I have removed the relation and tried both of these choices independently and they do work when they are on their own so that's not the issue. I have tried putting relation at the top, in the middle and nothing seems to work. Could it be AND doesn't work with custom taxonomies?

Thanks