The joomla article url's show the article id, the category and the section. This leads to canonical issues whenever the section or category changes. Same problem when a section/category menu is added or a site switches from non-SEF to SEF url's.
The article canonical plugin will put a canonical link in the header of the document, pointing search engine's to the right location:
<link href="http://www.affiliatefeeds.nl/en/47-datafeeds/3060-quick-guide.html" rel="canonical" />
Joomla 3.x has its own canonical system.