Stylesheets and dark/light mode handling

An application that sets a Stylesheet and switches at runtime between dark/light mode does not update all palette entries correctly for the new scheme. This is even the case if the whole stylesheet is commented out, which should result in the default palette. Clearing the stylesheet with `setStyleSheet("");` at runtime sets the palette entries back to the expected values. Fusion style seems to be more affected by this than Windows11 style. An example project is attached.