Problem appears to be related to the WP eshop plugin, more specifically when the eshop short code has been used to display "add to cart" for linked product.
A normal page with up to one "add to cart" is fine, example:
Pages that use the eshop short code simply do not to display addthis buttons at the foot of the page content, example:
Perhaps this is a known conflict, but I was unable to find anything when searching on the forum.
The code being used on the pages where addthis isn't working:
[eshop_show_product id="13988" panels="no" form="yes"]
I look forward to hearing from you.
Ed (Webmaster neverthebride.com)