get_category_link() and / or single_cat_title() not working in 3.0.1

[gazouteast]

As the title says ...

For verification, I have a fair number of sites all running the same theme, which has been layout tweaked to suit each one - the code in the templates remains the same on each other than layout and some CSS variations.

Under 2.9.2 (e.g at FlamingFood.com) you can see the category names and links in the grey bar at the head of each category's excerpts on the home page (view that first so you can see the example of it working)

Under 3.0.1 (e.g. at BuildaSkill.com/blog and GazLanNaThai.com/eye) - scroll down past the first 1/3 page to the category columns on those - the category titles do not display in the grey bar at the head of each group of category excerpts in each column.

I have checked and rechecked the code and there is no difference in the base block to create the category title and link. I've scoured the codex to find a deprecation notice and there is none. The category titles on the 3.0.1 sites did work under 2.9.2 (and all the way back to 2.5), but under 3.x they don't.

I have no idea why, but ​14161 might be related, ditto for ​13373 in which nacin describes get_category_link() as a WP_Error object - huh? It's a standard template tag according to the codex.

I've done all the usual debugging stuff and still cannot get this to return to the same functionality it displayed under 2.9.2 - it's also consistent across all my sites, the calling code in the home page template (index.php) is (using first column off gazlannathai.com) -

<?php
// enter the IDs of which categories you want to display
$display_categories = array(395);
foreach ($display_categories as $category) { ?>
    <div class="clearfloat">
      <div class="catwrap">
      <?php query_posts("showposts=10&cat=$category");
	    $wp_query->is_category = false;
		$wp_query->is_archive = false;
		$wp_query->is_home = true;
		 ?>
      <div class="cat-head">
        <h3><a href="<?php echo get_category_link($category);?>">
          <?php 
	// name of each category gets printed	  
	  single_cat_title(); ?>
          </a></h3>
      </div>
      <?php while (have_posts()) : the_post(); ?>
      <?php
// this grabs the image filename
	$values = get_post_custom_values("home-category-image");
// this checks to see if an image file exists
	if (isset($values[0])) {						
?>
      <a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title(); ?>"><img class="home-cat-img" src="<?php bloginfo('url'); echo '/'; echo get_option('upload_path'); echo '/'; $values = get_post_custom_values("home-category-image"); echo $values[0]; ?>" alt="image" /></a>
      <?php } ?>
      <h5><a href="<?php the_permalink() ?>" rel="bookmark" class="title">
      <?php 
// this is where title of the article gets printed	  
	  the_title(); ?>
      </a></h5>
      <?php the_content_rss('', TRUE, '', 50); ?><br /><br />
      <?php endwhile; ?>
      </div>
    </div>

That's the per category block / loop which appears in a column div - the other columns are the same but with more categories in the array and fewer posts per category.

As I said - it worked fine from 2.5 to 2.9.2, but is banjaxed in 3.0.x and everything is pointing to something in core in the two functions named in the title.

Gaz

[scribu]

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​http://wordpress.org/support/forum/how-to-and-troubleshooting