hi mozart
when you save an image in gimp, it usually produces a gimp file (with the extension .xcf) – if you like to have your image file auto updated in scribus, it has to replace the old file. (same file name, same file type and same place in the file system…)
if you save it this way (by overwriting the old file), you'll lose the unchanged file – so think about a backup first!
utnik