How delete item from one category without affecting another category?

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Hi,

I'm trying to tidy up an OSComm site and I've come across a strange anomalie: when a product upload was done via ezpopulate, there were typos in the .csv file, which created a duplicate category to put the new products into. The products have appeared in both the erronious folder and the correct folder (e.g. both "cap and tubes" and "caps and tubes" categories). When I try to remove the products from the "cap and tubes" erroneous category/folder, the product is also removed from the correct "caps and tubes" directory. Why is this and how do I separate the products so I can remove the erroneous folder but keep the correct folder and all its correctly-uploaded products intact?