Index: wp-includes/taxonomy.php
===================================================================
--- wp-includes/taxonomy.php	(revision 24807)
+++ wp-includes/taxonomy.php	(working copy)
@@ -1232,13 +1232,13 @@
 	extract($args, EXTR_SKIP);
 
 	if ( $child_of ) {
-		$hierarchy = _get_term_hierarchy($taxonomies[0]);
+		$hierarchy = _get_term_hierarchy(reset($taxonomies));
 		if ( !isset($hierarchy[$child_of]) )
 			return $empty_array;
 	}
 
 	if ( $parent ) {
-		$hierarchy = _get_term_hierarchy($taxonomies[0]);
+		$hierarchy = _get_term_hierarchy(reset($taxonomies));
 		if ( !isset($hierarchy[$parent]) )
 			return $empty_array;
 	}
@@ -1307,7 +1307,7 @@
 	if ( !empty( $exclude_tree ) ) {
 		$excluded_trunks = wp_parse_id_list($exclude_tree);
 		foreach ( $excluded_trunks as $extrunk ) {
-			$excluded_children = (array) get_terms($taxonomies[0], array('child_of' => intval($extrunk), 'fields' => 'ids', 'hide_empty' => 0));
+			$excluded_children = (array) get_terms(reset($taxonomies), array('child_of' => intval($extrunk), 'fields' => 'ids', 'hide_empty' => 0));
 			$excluded_children[] = $extrunk;
 			foreach( $excluded_children as $exterm ) {
 				if ( empty($exclusions) )
@@ -1416,20 +1416,20 @@
 	}
 
 	if ( $child_of ) {
-		$children = _get_term_hierarchy($taxonomies[0]);
+		$children = _get_term_hierarchy(reset($taxonomies));
 		if ( ! empty($children) )
-			$terms = _get_term_children($child_of, $terms, $taxonomies[0]);
+			$terms = _get_term_children($child_of, $terms, reset($taxonomies));
 	}
 
 	// Update term counts to include children.
 	if ( $pad_counts && 'all' == $fields )
-		_pad_term_counts($terms, $taxonomies[0]);
+		_pad_term_counts($terms, reset($taxonomies));
 
 	// Make sure we show empty categories that have children.
 	if ( $hierarchical && $hide_empty && is_array($terms) ) {
 		foreach ( $terms as $k => $term ) {
 			if ( ! $term->count ) {
-				$children = _get_term_children($term->term_id, $terms, $taxonomies[0]);
+				$children = _get_term_children($term->term_id, $terms, reset($taxonomies));
 				if ( is_array($children) )
 					foreach ( $children as $child )
 						if ( $child->count )