Forum module struggles - expert needed

It seems that it is difficult to get some help on the forum module.
Please also look at http://drupal.org/node/199424

I can see the whole structure of the forum and the number of contents.
BUT ...
if you get into the the forum topic, you can not see all the entries as shown in the forum overview.
This is strange...
(Overview number of contents is 5 - but the forum topic itself just presents 3 entries).

Additionally, you can see the "invisible" forum content in the "what's new" block of the forum AND, if you click on it, you can see the content. By the mean, the content IS available but not shown by the forum.

Very strange, isn't it?

By the way, I am using Drupal v5.5...

If you want to see it live you can get it on

http://www.soccer-wikki.info/?q=forum
(german site - but anyway it is easy to navigate through the forum)

Get into the forum: Turniere & Freundschaftsspiele
and you will see no entry!
BUT if you click on "Aktive Forenbeiträge" (Active) and "SpVg Koeln - Deutz 05 Sommercup 2008" (http://www.soccer-wikki.info/?q=content/spvg-koeln-deutz-05-sommercup-20...) you can see that the content is existend and located in the forum as mentioned above.

(See also http://drupal.org/node/170118#comment-674658)