This already happens if you edit the bitmaps with Photo-Paint and save them there. It can't happen if you use any other software to edit them because the bitmaps in Draw aren't dynamically-linked to files, they're properly imported. There are several suggestions here that would like images to be dynamic links instead but I'd be up a creek if I had to switch to that behaviour, if it's implemented I hope it's at least an option so that the default behaviour (copied in) could be preserved if chosen.
This already happens if you edit the bitmaps with Photo-Paint and save them there. It can't happen if you use any other software to edit them because the bitmaps in Draw aren't dynamically-linked to files, they're properly imported. There are several suggestions here that would like images to be dynamic links instead but I'd be up a creek if I had to switch to that behaviour, if it's implemented I hope it's at least an option so that the default behaviour (copied in) could be preserved if chosen.