The filepicker must adhere fully to the specs for the resource-type registration. In the case of attaching by copying, a resource can only be copied if a copy action is defined for the type. And then it must invoke the required methods.
One way to verify this is to attach a citation list to an assignment and then make changes to the citations in the original citation list (for example, add and remove citations, AND change the values of some fields in a few citations). If the changes show up in the copy attached to the assignment, this is not fixed. If none of the changes show up in the copy, that's pretty good evidence that this is fixed.