QComboBox::setItemData doesn't update data as expected..

[MachoX]

Here's the code:
@
class MyType
{
public:
QString key;
QString val;
bool operator==(const MyType& other) const
{
return key == other.key;
}

bool operator<(const MyType& other) const
{
    return key < other.key;
}

};

Q_DECLARE_METATYPE(MyType)

int main(int argc, char *argv[])
{
QApplication app(argc, argv);

qRegisterMetaType<MyType>("MyType");
    QMetaType::registerComparators<MyType>();

MyType mytype;
mytype.key = "abc";
mytype.val = "zxc";
QComboBox* cmb = new QComboBox();
cmb->addItem("123", QVariant::fromValue(mytype));

qDebug() << "key:" << cmb->currentData().value<MyType>().key << " val:" << cmb->currentData().value<MyType>().val;
//OutPut: key: "abc"  val: "zxc"

mytype.val = "vbn";
cmb->setItemData(cmb->currentIndex(), QVariant::fromValue(mytype));
qDebug() << "key:" << cmb->currentData().value<MyType>().key << " val:" << cmb->currentData().value<MyType>().val;
//OutPut: key: "abc"  val: "zxc"       Expected: key: "abc"  val: "vbn"

return app.exec();

}
@

Eventually I found out the trick by changing the implementation of the overridden comparator "==" into "{ return (key == other.key && val == other.val);}"
But that's another way of diverging from my expectation. As the members of MyType are so named, when using QComboBox::findData, as long as MyType::key matches, that's the data I want.
Is there any workaround about this?