Could you try echoing out that query instead of executing it? I.e. replace:
$result = $db->query('SELECT id, poster, subject, posted, last_post, last_post_id, last_poster, num_views, num_replies, closed, sticky, moved_to FROM '.$db->prefix.'topics WHERE forum_id='.$id.' ORDER BY sticky DESC, last_post DESC LIMIT '.$start_from.', '.$disp_topics) or error('Unable to fetch topic list for forum', __FILE__, __LINE__, $db->error());
with
dump('SELECT id, poster, subject, posted, last_post, last_post_id, last_poster, num_views, num_replies, closed, sticky, moved_to FROM '.$db->prefix.'topics WHERE forum_id='.$id.' ORDER BY sticky DESC, last_post DESC LIMIT '.$start_from.', '.$disp_topics);
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