Random no 1 appearing when using breadcrumbs

Hi,
Fantastic plugin, does exactly what I want… however when I implement it I get a random ‘1’ on the top of a post (Seems to be appearing just after the entry-meta.

(I use thematic and am calling it using a function in my child theme:

//Add Breadcrumb on top of single posts
function add_joost_breadcrumb($postheader) {
	if (is_single()) {
	if (function_exists('yoast_breadcrumb') )
	$postheader .= yoast_breadcrumb('<p id="breadcrumbs">','
');
	}
	return $postheader;
}
add_action ('thematic_postheader','add_joost_breadcrumb');

Any ideas how I can get rid of it?

Thanks
Dan