How do I prevent products showing up in multiple product categories when only categorized in one?

I am using MarketPress with the Weaver II WordPress theme. I have created product categories for Hummingbird Feeders, Fine Writing Instruments (which has subcategories of Ballpoints, Fountain Pens and Rollerballs). All of the pens and the hummingbird feeders show up when you click on the Hummingbird Feeder item in the Product menu. If you click on any of the sub-categories only the items that should be in there show up. How do I stop the pens showing up under the Hummingbird Feeder category. They have not been double categorized.

Thanks for the help.

Michael