Tooltip on widget_tag_cloud_args not working

Hello,

I noticed that one of the arugments in the widget_tag_cloud_args is no longer working. I didn’t notice when this stopped working, so it could be that this hasn’t worked in a couple versions of WordPress.

Specifically, it’s the tooltip that appears when you hover your mouse over a tag in the tag cloud in the front end; it no longer appears because the required HTML isn’t output to the browser.

Can somebody tell me if this is a bug in WP, or if I’m doing something incorrectly, or need to update my code after a recent WP update?

Here is my code.

add_filter ('widget_tag_cloud_args', 'my_tags');

function my_tags($args){
	$args['smallest'] = '12';
	$args['largest'] = '12';
	$args['format'] = 'flat';
	$args['separator'] = ', ';
	$args['orderby'] = 'count';	
	$args['order'] = 'DESC';
	$args['topic_count_text_callback'] = 'my_tag_tooltip';
	// The arg above is the one that seems to have stopped working.
	return $args;	
}

function my_tag_tooltip($count){
	return sprintf( _n( '%s blog post with this tag', '%s blog posts with this tag', $count ), number_format_i18n( $count ) );
}