I upgraded to 3.2.1.
In /wp-includes/feed-rss.php, this file generates your RSS feed.
You'll see the loop uses the_excerpt_rss(). So the Full Content setting it would appear will have no bearing on the RSS feed output. This should be made clearer, as I've never really delved deeper into what the code does before.
I'm sure there are plugins that change this default functionality, which I'm thinking that sample link you previously passed on might be using, or perhaps they've modified the below code to output the content instead.
<?php while (have_posts()) : the_post(); ?>
<title><?php the_title_rss() ?></title>
<description><![CDATA[<?php the_excerpt_rss() ?>]]></description>
<link><?php the_permalink_rss() ?></link>
<?php do_action('rss_item'); ?>
<?php endwhile; ?>
In the above code I changed:
A bit of refreshing later, it finally did show the changes. Check this link regarding the_content_rss function, as it warns the function has be deprecated, so in future upgrades if you rely on this it may be removed.
Hope this finally fixes your problem *fingers crossed*