When I delete posts from a forum (in this example some system generated artifacts for moved posts), and do that by [x] checking the messages and choosing "delete" from the drop-down list, I get a page full of SQL statements, like below:

UPDATE `jos_fb_categories` SET `time_last_msg`='1189170077',`id_last_msg`='191',`numTopics`='6',`numPosts`='4' WHERE `id`='1'

UPDATE `jos_fb_categories` SET `time_last_msg`='1189078998',`id_last_msg`='110',`numTopics`='2',`numPosts`='0' WHERE `id`='2'

UPDATE `jos_fb_categories` SET `time_last_msg`='0',`id_last_msg`='0',`numTopics`='0',`numPosts`='0' WHERE `id`='3'

UPDATE `jos_fb_categories` SET `time_last_msg`='0',`id_last_msg`='0',`numTopics`='0',`numPosts`='0' WHERE `id`='4'

UPDATE `jos_fb_categories` SET `time_last_msg`='1189078998',`id_last_msg`='110',`numTopics`='2',`numPosts`='0' WHERE `id`='5'

UPDATE `jos_fb_categories` SET `time_last_msg`='1188828020',`id_last_msg`='8',`numTopics`='1',`numPosts`='0' WHERE `id`='6'

UPDATE `jos_fb_categories` SET `time_last_msg`='1189170077',`id_last_msg`='191',`numTopics`='3',`numPosts`='4' WHERE `id`='7'

UPDATE `jos_fb_categories` SET `time_last_msg`='',`id_last_msg`='',`numTopics`='73',`numPosts`='172' WHERE `id`='8'

UPDATE `jos_fb_categories` SET `time_last_msg`='1189176792',`id_last_msg`='207',`numTopics`='13',`numPosts`='35' WHERE `id`='9'

UPDATE `jos_fb_categories` SET `time_last_msg`='1189346325',`id_last_msg`='263',`numTopics`='58',`numPosts`='131' WHERE `id`='10'

UPDATE `jos_fb_categories` SET `time_last_msg`='1189341663',`id_last_msg`='260',`numTopics`='36',`numPosts`='82' WHERE `id`='11'

UPDATE `jos_fb_categories` SET `time_last_msg`='0',`id_last_msg`='0',`numTopics`='0',`numPosts`='0' WHERE `id`='12'

UPDATE `jos_fb_categories` SET `time_last_msg`='1189341440',`id_last_msg`='259',`numTopics`='2',`numPosts`='6' WHERE `id`='13'

Go to class.fireboard.php Line 453
and delete
echo($database->getQuery());

Yes, that did the trick! Thank you!