[development] Why is drupal_page_footer() triggering cron?

Hi In D7 I discovered at the end of drupal_page_footer()[1] cron jobs are started. On our website this triggers the search index being updated, which can take minutes. Needles to say that the user doesn't want to wait for this to be finished. I'm curious whether cron is relay called at the end of each page request? My understanding of hook_cron is that it is only called by cron.php. How can I make sure that this does not trigger any long running cron jobs? Regards Ernst [1] http://api.drupal.org/api/drupal/includes--common.inc/function/drupal_page_f...