QGraphicsScene addItem with Smart Pointer - qt

Question

I have a problem using smart pointers with Qt. I can´t figure out what is the reason for that strange behaviour.
Simple Setup:
I created a new Qt Widgets Application and dragged a QGraphicsView into the main window and only added the following Code to paint a circle:
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "QGraphicsScene"
#include "QGraphicsEllipseItem"
#include "boost/shared_ptr.hpp"
#include "QSharedPointer"
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
QGraphicsScene* scene = new QGraphicsScene(ui->graphicsView);
ui->graphicsView->setScene(scene);
/* 1. raw pointer */
QGraphicsEllipseItem* ell = new QGraphicsEllipseItem(100,100,50,50);
scene->addItem(ell);
/* 2. boost shared pointer
boost::shared_ptr<QGraphicsEllipseItem> eSP(new QGraphicsEllipseItem(100,100,50,50));
scene->addItem(eSP.get());*/
/* 3. Qt shared pointer
QSharedPointer<QGraphicsEllipseItem> eSP(new QGraphicsEllipseItem(100,100,50,50));
scene->addItem(eSP.data());*/
/* 4a. raw pointer as init parameter for shared pointer
QGraphicsEllipseItem* ell = new QGraphicsEllipseItem(100,100,50,50);
boost::shared_ptr<QGraphicsEllipseItem> eSP(ell);
scene->addItem(eSP.get()); // using shared pointer */
/* 4b. raw pointer as init parameter for shared pointer
QGraphicsEllipseItem* ell = new QGraphicsEllipseItem(100,100,50,50);
boost::shared_ptr<QGraphicsEllipseItem> eSP(ell);
scene->addItem(ell); // using raw pointer */
}
MainWindow::~MainWindow()
{
delete ui;
}
As you can see I tried some variants. The first one ist the only one that works. It paints a circle in the center of the QGraphicsView. But for my project I need a smart pointer implementation. But all the smart pointer implementations do not paint the circle.
Am I making any mistake???
Especially 4b confuses me most. The only difference to 1 is that I am putting the raw pointer additionally into a shared pointer and that won´t work
Please help me!
My environment:
- Linux Mint 17.1
- qt-sdk 2ubuntu3
- boost 1.54.0.1