Hi,
on a product page we can render several lists of products related to the current product, what other customers have looked at etc.
All the products rendered here appear to have the same group id, namely that of the current product. So when the visitor clicks a product that is actually placed in a different group, it doesn't display correctly if you have a menu structure that indicates your "position" in the shop, so to speak.
Outputting AssociatedGroups showed the same ID that is used in the tag Ecom:Product.LinkGroup used for the link. So maybe the error is in the output of the loops, ie. GetLoop("eCom:Related.YouHaveSeenTheseProducts").
I hope I made my issue clear, otherwise I'll happily elaborate :)