QProxyStyle: When setting a style that is a subclass of QProxyStyle on a widget, then this will have the effect of influencing other widgets using that same base style. This is because in order for QProxyStyle to work, it calls setProxy() on the base style, therefore, if you did:

widget->setStyle(new MyProxyStyle(widget->style());

and the widget was using QApplication::style(). Then it will cause the whole application to be changed to use the proxy style.

Example is attached which shows both tableviews having horizontal headers with the style applied, but setStyle() was only called on one of them.