Frontend Clean URLs is sometimes generating backend URLs on pages with shortcodes

While setting up CiviEvent Calendar for a client I came across an odd situation where the event links were produced as backend links via a shortcode

How to Reproduce

1. Setup some Events
2. Install CiviEvent Calendar
3. Copy over the WP plugin and activate
4. Add a shortcode to a Page like Test
5. See the Events appear as https://mysite.org/?civiwp=CiviCRM&q=civicrm%2Fevent%2Finfo&id=27

What was expected

I thought that the URL would appear as a normal civicrm/event/info&id=27 link.

Other Details

I found one issue in their own extension that was no properly passing the url function properly so I fixed that. Even doing so it seems to not function properly. It is now

      $url = CRM_Utils_System::url('civicrm/event/info', // path
        'id=' . $dao->id ?? NULL, // query
        TRUE, // absolute
        NULL, // fragement
        FALSE, // htmlize
        TRUE, // Frontend
        FALSE // Backend
      );

They are doing the following code to generate the shortcode from their own code (note: I added the new url/base hook but that still didn't work

    // Call wp_frontend with $shortcode param.
    add_filter('civicrm/core/url/base', 'event_calendar_fixed_base_url');
    if (class_exists('CiviCRM_For_WordPress')) {
      civi_wp()->invoke();
      $content = ob_get_clean(); // save the output and flush the buffer
      return $content;
    }
    else {
      return civicrm_wp_frontend(TRUE);
    }
    remove_filter('civicrm/core/url/base', 'event_calendar_fixed_base_url');
  }
}

function event_calendar_fixed_base_url() {
  return  CRM_Utils_System::getBaseUrl(TRUE, TRUE, FALSE);
}

I narrowed the code down to this line. The $frontend_line gets set, but it's not the basepage. Then it's basically used farther down (I think) instead of the basePage even thought we asked for a FrontEnd link. I actually think that instead of the else here we should just remove it and do the check anyway, but this is complex logic so maybe I don't understand.

I wanted to report it to discuss a bit because A) maybe there is something wrong in the rendering for CiviEvents that is a quick fix or B) this is a bigger problem 🤷