I have actually done this with easy populate on character wrong in the category name will produce linked products.

The other problem may possibly be, which I have also run into, you can not use the same name of the file each time unless you delete it from your temp files first.

I have made both these mistakes to no avail. The fastest way of correcting the problem is to delete the offending entries in the database, but only do that if you know your database program well.