Windows 7 style overrides many qss settings. i.e. combo box background colour

The windows 7 style overrides the combobox background colour. We attempt to set this colour to red when invalid input is entered by changing the QPalatte::Base colour role using the "void setColor ( ColorGroup group, ColorRole role, const QColor & color )"-method of the combobox widget.

See the attached screenshots of the CADFEKO "Request S-Parameter dialog" how this does not change to red on Windows 7. If the windows theme is changed to "Classic" the problem disappears.