Occasionally fail to append DIV at the end of the post with filter the_content

Hi,
I am trying to append a div at the end of the content.
I succeed to do so in some wordpress blogs, but others simply do not add the div.
I tested and saw that the my_add_widget function is being invoked in all blogs – but the div is just not appended in some cases.

Example of blog that do succeed to append the div: http://www.mixedwaves.com/
Example of blog that fails to append the div:
http://www.motorbikenews.co.uk/video-samsung-honda-meet-the-raf/

Code:

function my_add_widget($content)
{
$linkToPost = get_permalink($post->ID);
$content .= ‘<div id=”ewidget_’. $post->ID .'”></div>’;
return $content;
}

add_filter(‘the_content’, ‘my_add_widget’);

Any idea why is that?

Best,
Anat.