When putting a window inside QWidget::createWindowContainer its wheelEvent is not called in Qt 5.9.2 for Windows MSVC 2015 32 bit
in Qt 5.7.1 MSVC 2013 and Qt 5.9.2 macOS wheel event is called fine
To reproduce run example application. When you move mouse cursor on the colored widget and use mouse wheel it should fill the widget with random color.
If you focus the list widget and then move mouse cursor on the colored widget and use mouse wheel, the colors will not change because wheelEvent is not called.