Something wrong with QGraphicsScene y-acxis

Question

I have a simple example with QGraphicsScene wrong behavior

#include "mainwindow.h"
#include "./ui_mainwindow.h"
#include <QGraphicsView>
#include <QGraphicsScene>
#include <QGraphicsView>
#include <QGraphicsItem>

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    QGraphicsScene * scene = new QGraphicsScene(this);
    ui->graphicsView->setScene(scene);
    //background
    ui->graphicsView->setBackgroundBrush(Qt::black);

    QLineF y_line(ui->graphicsView->sceneRect().center().x(), ui->graphicsView->sceneRect().center().y() - 100,
                  ui->graphicsView->sceneRect().center().x(), ui->graphicsView->sceneRect().center().y() - 550);

    QLineF x_line(ui->graphicsView->sceneRect().center().x() - 100, ui->graphicsView->sceneRect().center().y(),
                  ui->graphicsView->sceneRect().center().x() - 550, ui->graphicsView->sceneRect().center().y());

    scene->addLine(y_line, QPen(Qt::yellow));
    
    //add line X
    scene->addLine(x_line, QPen(Qt::green));
    ui->graphicsView->fitInView(ui->graphicsView->sceneRect());
}

MainWindow::~MainWindow()
{
    delete ui;
}

I uave this:

And this is ok, i think BUT

if i comment out add line X

i have this :

How you can see the line direction!! changed .

How somebody can explain this??? Wrong behavior i think? some bugs in Qt?