Extra CSS Class Not Working on Menu Shortcode (Video included)

I have found a small problem with the menu shortcode – when I add an extra CSS class to the shortcode it doesn’t appear in the HTML on the webpage. This problem is only happening for the menu shortcode. It works fine on the siblings shortcode.

So when I insert this shortcode:
[su_menu name="About Us Menu" class="extraclass"]
the class="extraclass" line doesn’t appear in the HTML, so the class doesn’t get applied.

Here is a video (1:40) to demonstrate the problem:
https://youtu.be/GjkmlSzJ9DA?hd=1

Can this be fixed? Thanks.

(I haven’t included a link to the actual site, because it is not publicly accesible yet).

https://www.ads-software.com/plugins/shortcodes-ultimate/