Problem using $post->post_title in loop = blank

I have some custom code that trims down the post title if its over so many characters, and this is the code that I use:

if (strlen($post->post_title) > 40) {
        $trimmedtitle = substr($post->post_title, 0, 60) . '...'; } else {
        $trimmedtitle = $post->post_title;
    }

This works fine when I view the listings/archive page without any ajax filters applied, and shows the post title correct.

However when I filter the results, the post title comes back blank. Everything else displays ok though.

If I change $trimmedtitle back to the_title(); then it works fine.

Why doesn’t this work when the results are pulled via ajax?

http://wordpress.org/plugins/ajax-wp-query-search-filter/