If you provided a category section in your product string, version 14 made a 1:1 association between the product and category.
For example:
s.products=category;product;quantity;price;...
In Version 14, the first category associated with a product in a calendar month would be tied to that product for the entire month.
Adobe Analytics/SiteCatalyst 15 allows multiple categories per product. If you have products in multiple categories in the product string, you might see different values in the category report than you did before.
Thanks,
Asheesh