Index: wp-includes/taxonomy.php
===================================================================
--- wp-includes/taxonomy.php	(revision 23447)
+++ wp-includes/taxonomy.php	(working copy)
@@ -1190,6 +1190,9 @@
 	if ( ! is_array( $taxonomies ) )
 		$taxonomies = array( $taxonomies );
 
+	// so that we can safely assume the array is 0-based
+	$taxonomies = array_values( $taxonomies );
+
 	foreach ( $taxonomies as $taxonomy ) {
 		if ( ! taxonomy_exists($taxonomy) ) {
 			$error = new WP_Error('invalid_taxonomy', __('Invalid taxonomy'));