If you have found that mousing over a category tag link under a post gives you a tip like:
"View all posts in Category1 rel="
it is because there is a missing double quote in template_functions_category.php
Line 58, after the line ---
$thelist .= '<a href="' . get_category_link($category->cat_ID) . '" title="' . sprintf(__("View all posts in %s"), $category->cat_name) . ' rel="category tag">';
There is a double quote missing before the rel attribute, near:
After the single quote we need a double quote so the HTML doesn't break.