That's because you are the 'from' person. If you are moving items from your sent items folder then by default you are the sender of that item. If you want the original senders name in there you would have to drag the message from your inbox, but, you would lose your reponse to that message. I don't believe you are able to change the senders name, and even if you were it would probably be a manual trawl to do it every time.
Regards
Ken...........