There are technical and logical reasons for not copying the relationships over in all cases: Keeping relations between items in different libraries won't work if you're e.g. copying an item from your library to a group, and it's related to other items in your library that won't be accessible to other members of the group. Copying the related items along with the items you dragged isn't necessarily what you want, either. And dropping the relations - what we do now - also clearly isn't ideal. We'll need a new interface to allow you to make that choice when you copy. But this is a known issue and a fix is planned.