.category-products is a marker for a subcat that has no subcats, only (possibly) products. It does not refer to actual product items. There is no error there.
Your mod is apparently built to display the products as well as categories in the sidebox. If you don't know enough PHP to modify its code, you can use another mod instead. Fragfutter's "Uncollapsed Category Tree" mod, hosted on his site and accessible from his thread in the forum, is reliable and easy to install, and will display all the categories and nothing else.
If you want more control over which categories display, use Categories Dressing from Free Addons.