QWSServer::setMaxWindowRect problem

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#include <QApplication>
#include <QLineEdit>
#include <QGridLayout>
#include <QPushButton>
#include <QWSServer>
 
int main(int argc, char* argv[])
{
	QApplication app(argc, argv);
    QPushButton button("hello world");
    QWSServer::setMaxWindowRect(QRect(100,100,200,200));
    button.showMaximized();
	return app.exec();
}

#include <QApplication>
#include <QLineEdit>
#include <QGridLayout>
#include <QPushButton>
#include <QWSServer>

int main(int argc, char* argv[])
{
	QApplication app(argc, argv);
    QPushButton button("hello world");
    QWSServer::setMaxWindowRect(QRect(100,100,200,200));
    button.showMaximized();
	return app.exec();
}

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when the application start, the application widget show normal on Geometry(100,100,200,200).
but when click the Restores button on the title bar.
the application widget show in 0,0 position.
but I have setMaxWindowRect(QRect(100,100,200,200)).

I wonder is it a bug?