Currently it is not possible to delete a Report which you have created by copying from another Report (if you did not have Delete rights on that one).
Often users copy from an existing Report and edit the way they need. So ultimately it is their Report. However, the system does not let them delete this own created Report. A Report created from scratch can be deleted by the user who has created it. The same should apply to copied Reports. The user who copied should be able to delete that Report copy.
