QSignalSpy crashes if signal is emitted from worker thread

#include <QtGui>
#include <QtTest/QtTest>

class Emitter : public QObject
{
    Q_OBJECT
public:
    Emitter()
    {
    }

    void emitSignal()
    {
        emit signal();
    }
signals:
    void signal();
};

class MyThread : public QThread
{
    Q_OBJECT
public:
    MyThread(Emitter *emitter)
        : m_emitter(emitter)
    {
    }

    ~MyThread()
    {
        wait(100);
    }

protected:
    void run()
    {
        for (int i = 0; i < 100; ++i) {
            m_emitter->emitSignal();
            msleep(100);
        }
    }

private:
    Emitter *m_emitter;
};

#include "main.moc"

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

    Emitter emitter;
    QSignalSpy spy(&emitter, SIGNAL(signal()));
    for (int t = 0; t < 5; ++t) {
        MyThread *thread = new MyThread(&emitter);
        thread->start();
        QObject::connect(thread, SIGNAL(finished()), thread, SLOT(deleteLater()));
    }
    QTest::qWait(20000);

    qDebug() << spy.count();

    return 0;
}