The newest Update (3.5.1) added several new features. The most requested feature was the Amazon Description. This is now on by default for products that use the old shortcode.
An additional feature was a NEW shortcode that has many more features. If you switch your old shortcodes to the new shortcode, the display should look more like it did prior to the update (i.e., no description). The old shortcode was set up like so
AMAZONPRODUCT=XXXXXXXXXX]. This is not ideal for adding features so the new shortcode uses the WordPress Shortcode system to process the shortcode, making it much easier for us to add parameters (or features) to the products via the shortcode. The NEW shortcode should be used like so:
if you decide you want the description in the new shortcode, you can turn it on by using:
AMAZONPRODUCTS asin="XXXXXXXXXX" desc=1]