Something stopping UNA RSS block on profile page from parsing dynamic RSS url

On my Dolphin site I have created an RSS block on the profile page and use an RSS URL with a parameter/variable (sorry not sure of correct term). This works perfectly and replaces the variable with the profile's username. I am wanting to move my site to UNA so I tried to set this same thing up with UNA but have run into a problem with using this dynamic RSS URL. 

On the UNA profile page, if I put the URL into a HTML or Raw box , adding the URL - (Domain(dot)com)/user/{display_name}/submitted/.rss will replace {display_name} with the profile owner's name to create a valid RSS URL - for example if I am viewing the profile page of a user named John, the url becomes, (Domain(dot)com)/user/John/submitted/.rss. This shows me that {display_name} works but I need the actual RSS feed to display, not just a link to it so I need this to work in the RSS box. Unfortunately,  if I put the same URL in an RSS box, {display_name} does not get replaced with the UNA username. So, while the UNA HTML and raw boxes parse the dynamic URL fine, something is stopping it from happening in the RSS box. Any thoughts on what might be the problem are appreciated.

Thank you.