We have made a new feature in the new version.
You will find a new checkbox on the plugin’s settings page: “Disable sub category display”. (Settings -> WooCommerce custom Tabs menu)
If you set it on, the tabs assigned to a sub category will not be displayed, if the main category is not set for the product. Please set this checkbox on.
You can download the new version in My Account menu of webshoplogic.com site:
Woocommerce Custom Tabs v1.0.10
We hope this accomplishes your claim.