Pot. regression 6.7 -> 6.8 QThreadPool too many thread IDs

#include <QCoreApplication>
#include <QThreadPool>
#include "qmutex.h"
#include "qtimer.h"

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    QThreadPool::globalInstance()->setExpiryTimeout(-1);
    QSet<int64_t> threadids;
    QMutex mutex;
    QTimer t;
    QObject::connect(&t,&QTimer::timeout,&t,[&threadids, &mutex]() {
        for(int i=0;i<10000;++i) {
            QThreadPool::globalInstance()->start([&threadids, &mutex]() {
                QMutexLocker locker(&mutex);
                threadids.insert(reinterpret_cast<int64_t>(QThread::currentThreadId()));
                qDebug()<<threadids.size();
            });
        }
    });
    t.start(1000);


    return   a.exec();
}