QTimer is stopped while screen is locked

[Fred]

I have just switched from Qt 4 to Qt 5.5 and found out that the behaviour of QTimer is different. When the session is automatically locked after 10 minutes of idle (Xubuntu / Light Locker) QTimer stops working and my application also stops working until the session is unlocked and the desktop appears.

I have tested the behaviour with this small app:

MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWindow)
{
 ui->setupUi(this);
 
 QTimer *timer = new QTimer(this);
 connect(timer, SIGNAL(timeout()), this, SLOT(update()));
 timer->start(1000);
}
 
void MainWindow::update(){
 ui->textEdit->append(QTime::currentTime().toString("hh:mm:ss"));
}

MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWindow)
{
 ui->setupUi(this);

 QTimer *timer = new QTimer(this);
 connect(timer, SIGNAL(timeout()), this, SLOT(update()));
 timer->start(1000);
}

void MainWindow::update(){
 ui->textEdit->append(QTime::currentTime().toString("hh:mm:ss"));
}

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And the timer stops after the session is locked:
13:43:01
13:43:02
13:43:03 <-- Session locked
13:43:36 <-- Session unlocked
13:43:37

Is this a bug or new feature? Qt 4.x works fine but Qt 5.5 do not. Is there a way to workaround this behaviour because my application also stop working while the session / screen is locked?