This cannot be fixed trivially. For example it is not clear what should happen when you have Line1, Line2, Line3 and delete Line2. Should the next line be named Line2 or Line4. How should we handle renamed planar figures during the generation of a new name. Therfore the current implementation seems to be okay. If you want to keep your drawn planar figures, you are supposed to rename them to whatever you just have drawn anyway.