setFocusProxy can cause asymmetric tab and shift+tab

#include <QApplication>
#include <QFrame>
#include <QPushButton>
#include <QVBoxLayout>

using namespace Qt::Literals::StringLiterals;

int main(int argc,char **argv){
	QApplication app(argc,argv);
	QWidget window;
	QVBoxLayout window_layout(&window);

	QFrame frame_1(&window);
	window_layout.addWidget(&frame_1);
	frame_1.setFrameStyle(QFrame::Box);
	QVBoxLayout frame_1_layout(&frame_1);

	QFrame frame_2(&frame_1);
	frame_1_layout.addWidget(&frame_2);
	frame_2.setFrameStyle(QFrame::Box);
	QVBoxLayout frame_2_layout(&frame_2);

	QPushButton button_1(u"button_1"_s,&window);
	window_layout.addWidget(&button_1);

	QPushButton button_2(u"button_2"_s,&frame_1);
	frame_1_layout.addWidget(&button_2);

	QPushButton button_3(u"button_3"_s,&window);
	window_layout.addWidget(&button_3);

	frame_1.setFocusProxy(&button_2);

	window.setVisible(true);
	return app.exec();
}

g++ f.c++ -o f -fno-plt -lQt6Core -lQt6Widgets -isystem /usr/include/x86_64-linux-gnu/qt6 -isystem /usr/include/x86_64-linux-gnu/qt6/QtWidgets

./f