Sorry, I'll try to explain the problem.
I have a history and geography class, a sub-category History of Europe and a sub-category of History of Europe,
Eastern Europe, Russia ( and other sub-categories of History of Europe )
Like this :
History and geography
|_ History of Europe
|_ Eastern Europe, Russia
|_ Central Europe, Germany
|_ British Isles
On the first page, I see the class history and geography with 0 books.
In the page of History and geography, I see History of Europe with 0 books.
And in the page History of Europe, I see the number of books in the category of Eastern Europe, Russia
it seems that the script counts the number of books in the sub-categories,
but only for a sub-category level.
I'll like to add something, in the admin zone , in the categories menu , we have the number of book
for the History of Europe category...