QString::append() weirdness

[mattc]

Hello,
does anybody know why in the following code 's' contains trash upon creation, but becomes valid after creating another QString?

#include <QApplication>
#include <QDebug>
 
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);  
 
    const QString& s = QString("hello").append("world");
    qDebug() << s; // s is invalid here (seen in the debugger)
 
    QString t = QString("hello").append("world");
    qDebug() << s; // s is ok (??????)
 
    return 0;
}

#include <QApplication>
#include <QDebug>

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

    const QString& s = QString("hello").append("world");
    qDebug() << s; // s is invalid here (seen in the debugger)
        
    QString t = QString("hello").append("world");
    qDebug() << s; // s is ok (??????)

    return 0;
}

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Qt 4.7
VS 2008 SP2
Vista