Smarter Navigation Breaking RSS Feed

I’m getting an error on my RSS feed page:

This page contains the following errors:
error on line 203 at column 1: Extra content at the end of the document
Below is a rendering of the page up to the first error.

When I examine the code, I see this error being added at the end of the code, after the closing </rss> tag:

Warning: Cannot modify header information – headers already sent by (output started at /wp-includes/feed-rss2.php:11) in /wp-content/plugins/smarter-navigation/main.php on line 74

The relevant line in feed-rss2.php is:

echo '<?xml version="1.0" encoding="'.get_option('blog_charset').'"?'.'>'; ?>

And looking at the plugin, it looks like that block of code is:

public function set_cookie( $data = '' ) {
		$data = wp_parse_args( $data, array(
			'query' => json_encode( $GLOBALS['wp_query']->query ),
			'url' => ( is_ssl() ? 'https://' : 'http://' ) . $_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI'],
			'title' => trim( wp_title( self::SEP, false, 'left' ) ),
		) );

		foreach ( $data as $key => $value )
			setcookie( self::get_name( $key ), $value, 0, '/' );
	}

The setcookie line near the bottom is line 74. Is there a way to tell it to not try to set the cookie if it’s on the RSS page? Or is something else causing the problem? I know that blank lines at the beginning or end of files can cause these types of problems, but that doesn’t seem to be the issue in this case.

When I disable the Smarter Navigation plugin, the RSS works again.

I really love the Smarter Navigation plugin, but I need my RSS feed to work. Any help would be much appreciated!

Thanks.

http://wordpress.org/plugins/smarter-navigation/