Index: wordpress/wp-includes/taxonomy.php
===================================================================
--- wordpress/wp-includes/taxonomy.php	(revision 21204)
+++ wordpress/wp-includes/taxonomy.php	(working copy)
@@ -1759,6 +1759,8 @@
 		if ( $defaults['default'] == $term )
 			return 0; // Don't delete the default category
 	}
+	elseif ( apply_filters( 'wp_default_term_' . $taxonomy, false, $term ) )
+		return 0; // Don't delete the default term
 
 	$args = wp_parse_args($args, $defaults);
 	extract($args, EXTR_SKIP);
 
 /**