That's a very weird bug, but very annoying as well for any editing application (text, picture, audio, video...).

It's OSX specific (testing with 10.9).

When a QFileDialog is shown, any Edit menu with actions named "Cut", "Copy", "Paste" or "Select All" or some other very common name are disabled !

Repro with Qt 5.4 beta SDK:
Open the Qt5.4.0/Examples/Qt-5.4/widgets/mainwindows/mainwindow example.
in void MainWindow::setupMenuBar(), change to:

    mainWindowMenu = menuBar()->addMenu(tr("Edit"));

    action = mainWindowMenu->addAction(tr("Select All"));
    action->setCheckable(true);
    action->setChecked(dockOptions() & AnimatedDocks);
    connect(action, SIGNAL(toggled(bool)), this, SLOT(setDockOptions()));

    action = mainWindowMenu->addAction(tr("Cut"));
    action->setCheckable(true);
    action->setChecked(dockOptions() & AllowNestedDocks);
    connect(action, SIGNAL(toggled(bool)), this, SLOT(setDockOptions()));

(I just renamed a menu and few of its action)

Then build and launch the application, click File/Save Layout or File/Load Layout, cancel that dialog, and see the content of the "Edit" menu: the "Cut" and "Select All" actions have been disabled ! Plus, there's no way to re-enable them...

The following Menu/Action seems to be affected:
Edit/Cut
Edit/Copy
Edit/Paste
Edit/Select All
...and maybe others.