I'm having this error today on a live wordpress 3.0. The site is on the web, but hasn't been launched yet.
I have three loops with multiple taxonomies on one page. When there are results, they are shown correctly. When there aren't results, a random 13 (??) posts that don't match either criteria are shown, instead of no result.
Here's the code for one of the loops:
<h3 class="events">Text Studies & Lesson Plans Tagged '<?php echo $term->name; ?>'</h3>
<?php if ( have_posts() ) : while ( have_posts() ) : the_post(); ?>
<p><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></p>
<?php endwhile; else: ?>
<p><?php _e('There are no lesson plans tagged with'); ?> '<?php echo $term->name; ?>'</p>
<?php endif; //end news?>