The default value of isPermaLink is true, not including it does nothing.

http://www.rssboard.org/rss-specification#ltguidgtSubelementOfLtitemgt

diff --git a/includes/Feed.php b/includes/Feed.php
index a80e6b7..bd03901 100644 (file)
--- a/includes/Feed.php
+++ b/includes/Feed.php
@@ -305,7 +305,7 @@ class RSSFeed extends ChannelFeed {
                <item>
                        <title><?php print $item->getTitle() ?></title>
                        <link><?php print $item->getUrl() ?></link>
-                       <guid<?php if( $item->RSSIsPermalink ) print ' isPermaLink="true"' ?>><?php print $item->getUniqueId() ?></guid>
+                       <guid<?php if( !$item->RSSIsPermalink ) print ' isPermaLink="false"' ?>><?php print $item->getUniqueId() ?></guid>
                        <description><?php print $item->getDescription() ?></description>
                        <?php if( $item->getDate() ) { ?><pubDate><?php print $this->formatTime( $item->getDate() ) ?></pubDate><?php } ?>
                        <?php if( $item->getAuthor() ) { ?><dc:creator><?php print $item->getAuthor() ?></dc:creator><?php }?>