not good. looks like in DocumentManager::doSaveAs, we do detect if file writing failed, but the only feedback is a debug message printed to stderr:

QFile file(path);
if(!file.open(QIODevice::WriteOnly)) {
    qWarning() << "DocumentManager: the file" << path << "could not be opened for writing.";
    return false;
}

DocumentManager::doSaveAs and returns a boolean that indicates whether saving was successful. so does MainWindow::save. however, the methods MainWindow::saveDocument and MainWindow::saveDocumentAs do not provide any user feedback if saving failed. MainWindow::save does detect for a few problematic file-saving cases like the cases where a file itself is not writable, but it only asks for permission, never forgiveness -- so any failure that we didn't anticipate is silently ignored. luckily the fix seems simple. not so simple is refactoring the saving code so that it's not all 90% awkwardly stuffed in MainWindow::save.