QThread, two QTimer's and QMutex deadlock

Question

I have QObject with method, protected with QMutex. This method can be directly run from many threads. And I have another QObject living in other QThread with two QTimers. Timers have different intervals and on timeout() call method of first object.

It may occure, that timers expire simultaniously and lock the same QMutex from the same thread. How can It be possible? Why one QThread run code parallel with itself?

I eliminated this issue by putting timers in different threads. But why QThread can execute code by this way?

void Module::exec(const QString command)
{
    qDebug("---> run from %X", QThread::currentThreadId());
    QMutexLocker lock(&m_mutex);
    //do the work    
}

class AutoCalibration : public QObject
{
    Q_OBJECT
public:
    explicit AutoCalibration(QObject *parent = 0);
protected:
    QTimer *m_timerTimeout;
    QTimer *m_timerPolling;
    QThread *m_worker;
}

AutoCalibration::AutoCalibration(QObject *parent) : QObject(),
    m_timerTimeout(new QTimer()),
    m_timerPolling(new QTimer()),
    m_worker(new QThread(parent))
{
    m_timerTimeout->moveToThread(m_workwr);
    m_timerTimeout->setInterval(15000);

    m_timerPolling->moveToThread(m_workwr);
    m_timerPolling->setInterval(10000);

    connect(m_timerTimeout, &QTimer::timeout, this, &AutoCalibration::calibrate, Qt::DirectConnection); // run Module::exec() with one argument
    connect(m_timerPolling, &QTimer::timeout, this, &AutoCalibration::requestProp, Qt::DirectConnection); // run Module::exec() with another argument

    connect(m_worker, &QThread::finished, m_timerTimeout, &QTimer::stop);
    connect(m_worker, &QThread::finished, m_timerPolling, &QTimer::stop);

    connect(m_worker, SIGNAL(started()), m_timerTimeout, SLOT(start()));
    connect(m_worker, SIGNAL(started()), m_timerPolling, SLOT(start()));

    m_worker->start();
}