Subcategories are not shown

As far I can see, when one only chose the main category in the email preferences, then its subcategories are not shown in the Newsletter (MailAlert). This seems to apply to both Latest Articles as well as to Latest Post in Kunena. I would like to set up the two plugins for the Articles and the Posts in such a way where the users only can select the main categories and then the content in their subcategories will be included automatically in the Newsletter.

It's very impractical and becomes confusing then both the main and sub categories has to be chosen, especially in a multilingual web site.