For saving, yEd first writes the diagram to a new temporary file with an arbitrary name, then deletes the original file, and finally renames the temporary file to the original name. The idea of this process is that the original file remains unchanged if the writing in step one fails. Unfortunately, we don't check the 'write-protected' attribute of the original file and it seems to be no problem to delete a 'write-protected' file in Windows. (At least, it's no problem to delete such files in Windows Explorer.)