Why does my toolbar dock to the incorrect location?

Question

I have a weird scenario. I create a QMainWindow that is embedded in a QGraphicsScene. I want to have multiple QMainWindows each with a toolbar inside the scene. I'm simulating an MDI Area, without using the QMdiArea class.

Here is the MainWindow.cpp

#include "mainwindow.h"


MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent){
    resize(1000, 750);
    qApp->setStyle(QStyleFactory::create("Fusion"));

    QGraphicsView* view = new QGraphicsView;
    QGraphicsScene* scene = new QGraphicsScene;
    view->setFixedSize(1000, 750);
    view->setScene(scene);
    view->scene()->setSceneRect(-150, -150, view->size().width(), view->size().height());

    setCentralWidget(view);

    QWidget* widget = new QWidget;
    widget->resize(300, 300);
    QVBoxLayout* vLay = new QVBoxLayout;

    widget->setLayout(vLay);

    QMainWindow* testWindow = new QMainWindow;
    testWindow->resize(300, 300);

    QToolBar* toolbar = new QToolBar;
    toolbar->setFloatable(false);
    toolbar->setStyleSheet("border: 1px solid red"); //For better seeing the issue
    toolbar->addAction("Test");

    testWindow->addToolBar(toolbar);
    vLay->addWidget(testWindow);

    scene->addWidget(widget);
}

What happens is the QToolBar will spawn in the correct location on the embedded QMainWindow, but when it's moved and docked anywhere, it will snap too far up and too far to the left. I've added outliner code to outline the toolbar so you can see the toolbar box.

Here is the MainWindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QGraphicsScene>
#include <QGraphicsView>
#include <QToolBar>
#include <QVBoxLayout>

class MainWindow : public QMainWindow{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = 0);

};

#endif // MAINWINDOW_H

Why does the toolbar do this weird snapping effect? I added the QMainWindow into a QWidget on purpose, as it's needed for something I'm doing. I realize that embedding just the QMainWindow has the desired interaction, but I need it embedded in the QWidget. I also realize that not having parents are bad for memory management, but I handle that as well.

I'm on Qt Version 5.10.1 and I'm using Redhat as my OS.