Some activities not displayed in contact summary "Activities" tab where there are activities "With" multiple contacts

This happens for contacts where there are activities that are "With" multiple contacts. Somehow, all of the other "With" contacts are counted within the 25 (or whatever) to be shown. This restricts the list of activities shown beneath such an activity.

If you go into the demo site (http://drupal.demo.civicrm.org/) and look at the activities under "Test Registrant", you'll see that I've put a phone call activity in there with lots of people and the activities below it are not shown:
http://drupal.demo.civicrm.org/civicrm/contact/view?action=browse&reset=1&cid=103&selectedChild=activity

This is detailed in http://forum.civicrm.org/index.php?topic=21005.new