QVariant can't save QWidget Pointer ?!!

[srazi]

I get problem when converting a QWidget* to QVariant, please see the following code and its output:

#include <QApplication>
#include <QWidget>
#include <QVariant>
#include <QDebug>
 
int main(int argc, char *argv[])
{
	QApplication a(argc, argv);
	QWidget *widget= new QWidget();
	QObject *obj = widget;
 
	  //you can use all other methods like qVariantFromValue(widget)
	QVariant var1 = QVariant::fromValue(widget);
	QVariant var2 = QVariant::fromValue(obj);
 
	qDebug() << "widget-addr=" << widget << "address saved to variant=" << var1;
	qDebug() << "object-addr=" << obj << "address saved to variant=" << var2;
}

#include <QApplication>
#include <QWidget>
#include <QVariant>
#include <QDebug>

int main(int argc, char *argv[])
{
	QApplication a(argc, argv);
	QWidget *widget= new QWidget();
	QObject *obj = widget;
	   
	  //you can use all other methods like qVariantFromValue(widget)
	QVariant var1 = QVariant::fromValue(widget);
	QVariant var2 = QVariant::fromValue(obj);
	
	qDebug() << "widget-addr=" << widget << "address saved to variant=" << var1;
	qDebug() << "object-addr=" << obj << "address saved to variant=" << var2;
}

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output:

widget-addr= QWidget(0x347748) address saved to variant= QVariant(QWidget*, )
object-addr= QWidget(0x347748) address saved to variant= QVariant(QObject*, QWidget(0x347748) )

Why line 13 doesn't work? Why it doesn't convert QWidget* to QObject* automatically? [I'm using Qt-4.7.3 and minGW]