Index: wp-includes/taxonomy.php
===================================================================
--- wp-includes/taxonomy.php	(revision 15704)
+++ wp-includes/taxonomy.php	(working copy)
@@ -2795,11 +2795,15 @@
 /**
  * Get an array of ancestor IDs for a given object.
  *
+ * @since 3.0.0
+ *
  * @param int $object_id The ID of the object
  * @param string $object_type The type of object for which we'll be retrieving ancestors.
+ * @param string $resource_type. (Optional).  Forces the resource type used (post_type or taxonomy)
+ *	to overcome ambiguities.
  * @return array of ancestors from lowest to highest in the hierarchy.
  */
-function get_ancestors($object_id = 0, $object_type = '') {
+function get_ancestors($object_id = 0, $object_type = '', $resource_type = null ) {
 	$object_id = (int) $object_id;
  
 	$ancestors = array();
@@ -2808,13 +2812,19 @@
 		return apply_filters('get_ancestors', $ancestors, $object_id, $object_type);
 	}
 		
-	if ( is_taxonomy_hierarchical( $object_type ) ) {
+	if ( 
+		'taxonomy' == $resource_type || 
+		( null === $resource_type && is_taxonomy_hierarchical( $object_type ) )
+	) {
 		$term = get_term($object_id, $object_type);
 		while ( ! is_wp_error($term) && ! empty( $term->parent ) && ! in_array( $term->parent, $ancestors ) ) {
 			$ancestors[] = (int) $term->parent;
 			$term = get_term($term->parent, $object_type);
 		}
-	} elseif ( null !== get_post_type_object( $object_type ) ) {
+	} elseif ( 
+		'post_type' == $resource_type || 
+		null === $resource_type && null !== get_post_type_object( $object_type ) 
+	) {
 		$object = get_post($object_id);
 		if ( ! is_wp_error( $object ) && isset( $object->ancestors ) && is_array( $object->ancestors ) ) 
 			$ancestors = $object->ancestors;
Index: wp-admin/admin-ajax.php
===================================================================
--- wp-admin/admin-ajax.php	(revision 15704)
+++ wp-admin/admin-ajax.php	(working copy)
@@ -560,7 +560,7 @@
 
 	$level = 0;
 	if ( is_taxonomy_hierarchical($taxonomy) ) {
-		$level = count( get_ancestors( $tag->term_id, $taxonomy ) );
+		$level = count( get_ancestors( $tag->term_id, $taxonomy, 'taxonomy' ) );
 		ob_start();
 		$wp_list_table->single_row( $tag, $level );
 		$noparents = ob_get_clean();