if both drawings are in different folders the arrow may be stored locally. If they are in the same folder I can only assume that the source file got deleted after inserting it in the working drawing. That drawing may contain the only copy of it so now sounds like a good time to WBLOCK it from that drawing to your library folder.
Another thought, could the working drawing have been created on a different log in? As you are storing things on your C drive it could be hidden from you but available to a different user. And as you are storing files on your C drive I hope you have a good back-up system in place.