Consider the following:

QLabel *label = new QLabel("foobar");
QGraphicsScene *scene = new QGraphicsScene;
scene->addWidget(label, Qt::Window);

The expected result is that the embedded label is shown with a window frame.

The actual result is that the embedded label is shown without a window frame.

QGraphicsScene::addWidget() calls setWidget() on the graphics proxy widget, which overrides any window flags passed to addWidget().

Workaround: set the window flags on the graphics proxy widget after it has been constructed.