Error in Products Navigation

[red0101]

Hi all,
when i browse the products details through the previous-next buttons, some products are skipped.
It happens on all templates, on all categories, using all sorting criteria, with SEO enabled or disabled.
As you can see in the attachment, we are in the product FS-1105 details and the next product is the FS-1107, not the FS-1106 as shown in the category list.

Joomla 2.5.2 and VM 2.0.2 upgraded (no error messages) from J 1.7.3 and VM 2.0

thanks

[attachment cleanup by admin]