crash when trying to make unvisible the mac os x oblong button when using unified window un title bar

When using these windows flags

Qt::WindowFlags flags = ( Qt::Window | Qt::CustomizeWindowHint ) & ~Qt::MacWindowToolBarButtonHint; the application crash at startup.

Error: objc[3397]: FREED(id): message insertItemWithItemIdentifier:atIndex: sent to freed object=0x6319230

In contrary, it does not crash (and works correctly) when using :

Qt::WindowFlags flags = Qt::Window | Qt::CustomizeWindowHint | Qt::WindowTitleHint | Qt::WindowSystemMenuHint | Qt::WindowMinMaxButtonsHint | Qt::WindowCloseButtonHint;
flags &= ~Qt::MacWindowToolBarButtonHint;

Once flags seted using setWindowFlags().

Create a main window with unified window and title bar and add toolbar at top with some actions.
The app crash with first method, and not with the second methode.