do_feed() causes duplicate feed content

I was encountering an issue where all of my RSS feeds contained duplicate information. I figured out the issue was not with the data itself, but that something was causing the feed output to be generated twice before output to the client.

I found the culprit in Magic Fields 2. Line 318, in main.php calls the do_feed() function. Here’s the full block of code:

// Process feeds and trackbacks even if not using themes.
  if ( is_robots() ) :
    do_action('do_robots');
    return;
  elseif ( is_feed() ) :
    do_feed();
    return;
  elseif ( is_trackback() ) :
    include( ABSPATH . 'wp-trackback.php' );
    return;
  endif;

When commenting this the one line with do_feed(), everything works as intended.

Question for the author: Why was this needed?

https://wordpress.org/plugins/magic-fields-2/