in wpbusdirman-category.php, look for the line
wpbusdirman_catpage_query();
just before the loop starts and comment it out. It should solve the issue but I think that it sacrifices the ability to display excerpts. Luckily I don’t need it 🙂
If you are ambitious, the problem lies in the query generated in wpbusdirman_catpage_query() having incorrect conditions hence yielding 0 results all the time.