Defaulting of catalogs in item creation

Hi we have both functional area catalogs and other catalogs. If an item is created from scratch, then the functional area catalogs are defaulted by functionality. In order to make other catalogs also to default while item creation , we have used Item rule sets to default the catalog category. But when this item rule set is present , if a user wants to create an item from an existing item, and in that process if user is also giving specifications as well as catalogs field, then when we click on save we are getting an error that-

Items cannot be assigned to multiple catagories for this catalog because the catalog is configured for single assignment category assignment.