I am using the yui-mainstream as a starting point, and further skinning it for my use.
Template changes have been very minimal, with most formatting and layout done in the css.
At some point a bug presented itself where when I am on the homepage and I click on a single post to go to that posts permalink, the result is a page with the proper permalink url, but it displays all published posts. Each post has the proper attributes as specified in the_loop (custom field values, etc), the trackback and rss urls are correct, the comment link is the clicked posts #respond url.
What could produce this???