[Mac Regression] Qt::Popup doesn't work correctly with other Qt::WindowFlags

I have a QDialog widget on which I set the following window flags:

_popupDialog->setWindowFlags(Qt::CustomizeWindowHint | Qt::WindowTitleHint | Qt::WindowStaysOnTopHint | Qt::Popup);

I also enable the size grip for the dialog.

When I show that dialog using Qt 4, I get a popup dialog with a title bar and a size grip. Using Qt 5 (I have only tested 5.4-dev) I get a window without a title bar that is not resizable.

I have attached screenshots showing this behavior and I've attached a sample application that demonstrates the problem.

I have also attached a screenshot of an example of how we are using this kind of widget in our application. The ability to move and resize this popup window is important in our application. The screenshot was taken using Qt 4.8.6.

This incorrect behavior appears to come from QCocoaWindow::windowStyleMask(Qt::WindowFlags flags) in qcocoawindow.mm where there is this code:

    if ((type & Qt::Popup) == Qt::Popup) {
        if (!windowIsPopupType(type))
            styleMask = (NSUtilityWindowMask | NSResizableWindowMask | NSClosableWindowMask |
                         NSMiniaturizableWindowMask | NSTitledWindowMask);
    } else {

The net effect is that all Qt::WindowFlags set on the window via QWidget::setWindowFlags() are ignored if the window's type is Qt::Popup.