Hi, thank you for this plugin.
I have a bit of a funny. If I start the drilldown with a hierarchical taxonomy that it loses it when I got any other taxonomy -ieL I get "OR" functionality, and the sign stays '+'.
If I start drilldown with a non-hierarchical taxonomy, then I can click on the hierarchical and do an "AND", and the hierarchical taxo gets a '-'.
I don't know whether this is intended functionality or not, but seems a bit unexpected.
I test with all messages on and at one stage got:
Notice: Array to string conversion in C:\web\wpbeta\wp\wp-content\plugins\query-multiple-taxonomies\widget.php on line 241