wp_tag_cloud Possible Bug

When I try to add a filter to wp_tag_cloud for use this function in the default widget, an error ocurrs:

I’m doing this in my functions.php file in my current template:

function tag_cloud_template($args) {
	$args['number'] = 15;
	$args['format'] = 'list';
	return $args;
}
add_filter('wp_tag_cloud','tag_cloud_template');

Then I get this on the frontend AND in the backend in the “edit-tags.php?taxonomy=post_tag” page.

1a href='http://MYSITE/wp-admin/edit-tags.php?action=edit&taxonomy=post_tag&post_type=post&tag_ID=16' class='tag-link-16' title='1 topic' style='font-size: 8pt;'>B&B

B&B is the first tag, there is a number “1” instead the “<” in the “<a” tag. The second tag it comes fine:

1a href='http://MYSITE/wp-admin/edit-tags.php?action=edit&taxonomy=post_tag&post_type=post&tag_ID=16' class='tag-link-16' title='1 topic' style='font-size: 8pt;'>B&B</a>
<a href='http://MYSITE/wp-admin/edit-tags.php?action=edit&taxonomy=post_tag&post_type=post&tag_ID=29' class='tag-link-29' title='1 topic' style='font-size: 8pt;'>beautiful views</a>
<a href='http://MYSITE/wp-admin/edit-tags.php?action=edit&taxonomy=post_tag&post_type=post&tag_ID=6' class='tag-link-6' title='5 topics' style='font-size: 15.466666666667pt;'>Bed and Breakfast</a>

If I remove the add_filter in the functions.php the error just gone.

If I try to use a separator like this:

function tag_cloud_template($args) {
	$args['separator'] = '-';
	return $args;
}
add_filter('wp_tag_cloud','tag_cloud_template');

then the output in the frontend and the backend is:
-a href='http://MYSITE/wp-admin/edit-tags.php?action=edit&taxonomy=post_tag&post_type=post&tag_ID=16' class='tag-link-16' title='1 topic' style='font-size: 8pt;'>B&B

so, maybe the error is in the separator filter, but the error occurs even if I dont’ use the separator arg.