Tinymce does not create the expected output

I have two sites running, both Drupal 6.14, same modules, same themes.
In on of them, Tinymce 3.2.7 works just fine, the way it is to be expected
In the other one, the same Tinymce, same settings, show up fine in the Edit-mode, al headings seem to be ok, but when I publish the page, no formatting is applied, no line breaks are made, no pictures show up, in other words, nothing that Tinymce was supposed to do works.
Any idea what went wrong, anyone? I've been searching for hours, but I really have no idea where to look next.

Thanks for replying,
Luk.