Accessing a forum (with forum topics) issues a php notice (warning)

Environment Details

PHP - 5.2.3
Apache - 2.2.3
Drupal - drupal-6.x-dev
OS - Linux (Fedora Core 6)

Steps to reproduce
1 - Enable Forum module

2 - Create a new Forum ("Running")

3 - Access the forum (http://www.testsite8.com/forum/7)
Since there are no forum topics in forum/7 it shows and empty table.

4 - Add a forum topic to forum 7 (http://www.testsite8.com/node/add/forum/7)

5 - Access the forum again (http://www.testsite8.com/forum/7)

it shows a notice
"notice: Undefined property: stdClass::$last_reply in /work/projects/testsites/drupal/6.x/testsite8/www/modules/forum/forum.module on line 769."

see attached screenshot.