I've noticed that when using MarbleWidget in my app, closing the top level widget will no longer quit the QApplication. This is because the PopupLayer is still alive and has Qt::WA_QuitOnClose set, but is never closed.

When unsetting it, MarbleWidget can be used in a window without having to set Qt::WA_DeleteOnClose. This allows the window to be created on the stack - also how it's done in Qt's examples: https://doc.qt.io/qt-5/qtwidgets-mainwindows-application-example.html