In windows 7 hover QPushButton by mouse increases memory usage.

 
//-- widget1.h
class Widget1 : public QWidget
{
 Q_OBJECT
private:
 void callWidget2();
public:
 Widget1(QWidget* parent = 0);
 ~Widget1() {}
 
};
 
//-- widget1.cpp
Widget1::Widget1(QWidget* parent)
 :QWidget(parent)
{
 QPushButton* btn = new QPushButton(this);
 btn->setText("show widget2");
 connect(btn, &QPushButton::clicked, this, &Widget1::callWidget2);
 
 this->resize(100, 100);
 
 this->show();
}
 
void Widget1::callWidget2()
{
 new Widget2();
}
 
//-- widget2.h
class Widget2 : public QWidget
{
 Q_OBJECT
private:
 
public:
 Widget2(QWidget* parent = 0);
 ~Widget2() {}
 
};
 
//-- widget2.cpp
Widget2::Widget2(QWidget* parent)
 :QWidget(parent)
{
 this->setAttribute(Qt::WA_DeleteOnClose);
 this->resize(300, 300);
 
 QPushButton* button = new QPushButton(this);
 button->setText("btn1");
 
 button = new QPushButton(this);
 button->setText("btn2");
 button->move(0, 20);
 
 button = new QPushButton(this);
 button->setText("btn3");
 button->move(0, 40);
 
 button = new QPushButton(this);
 button->setText("btn4");
 button->move(0, 60);
 
 button = new QPushButton(this);
 button->setText("btn5");
 button->move(0, 80);
 
 this->show();
}
 
//-- main.cpp
int main(int argc, char *argv[])
{
 QApplication a(argc, argv);
 
 //a.setStyle(new QWindowsStyle); // it solves the problem but looks bad.
 new Widget1;
 
 return a.exec();
}