If there are categories of 3 levels count is wrong
See example:

www.casasycosas.com.es/index.php?option=com_k2&view=itemlist&task=category&id=12:inmuebles-en-espa% C3% B1a&Itemid=180

There are altogether 14 articles, 6 in the "Catálogo Chalets" and 8 in the "Catálogo de pisos"
However, in the latter category ("Catálogo de pisos")daughter sum total of all items (14).

Click on "Catálogo pisos (14)" and you will see that the count is accurate or 8 items if there are 2 levels.