Black diamond in short description

Hi everybody,
sorry for my english...

I have a short description of the product in the summary of categories. But when the last symbol is with diacritics, it shows black diamond with question mark.
I have this in the .../catalog/controller/product/category.php to show the description:
'description' => strip_tags(mb_substr(html_entity_decode($result['description'], ENT_QUOTES, 'UTF-8'),0,150, 'UTF-8'))."...",

Is some mistake there?

Thanks...

you have to include <meta content="text/html; charset=utf-8" http-equiv="Content-Type" /> on you code.