Index: update.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/update/update.module,v
retrieving revision 1.23
diff -u -r1.23 update.module
--- update.module	17 Sep 2008 07:11:59 -0000	1.23
+++ update.module	17 Sep 2008 19:49:47 -0000
@@ -276,7 +276,9 @@
 function update_cron() {
   $frequency = variable_get('update_check_frequency', 1);
   $interval = 60 * 60 * 24 * $frequency;
-  if (REQUEST_TIME - variable_get('update_last_check', 0) > $interval) {
+  // Cron should check for updates if there is no update data cached or if the configured
+  // update interval has elapsed.
+  if (!cache_get('update_info', 'cache_update') || REQUEST_TIME - variable_get('update_last_check', 0) > $interval) {
     update_refresh();
     _update_cron_notify();
   }