Native QWindow based OpenGL/Vulkan windows positions are wrongly offset inside QMdiSubWindow

When assigning a QWindow derived window to a MdiSubWindow, its position gets offset to the left and top by the width of the window frame, which is 8 pixels exactly, this happens even when the sub window is maximized and there is no frame or border. Setting the window as main window or as a child of a layout on a non MDI widget does not show this behavior.

I am creating this bug report after finding no work around.

This is the code that creates the Sub Window:

// code placeholder
void MainWindow::on_actionOpen_triggered()
{
QString filename = QFileDialog::getOpenFileName ( this,
tr ( "Open Model" ),
tr ( "" ),
tr ( "Model Files (*.mdl *.txt)" ) );
if ( ! ( filename.isEmpty() || filename.isNull() ) )
{
QFileInfo fileinfo ( filename );
EngineWindow* window = new EngineWindow ( mRenderer );
QMdiSubWindow*
mdiSubWindow = mdiArea->addSubWindow ( QWidget::createWindowContainer ( window, mdiArea ) );
mdiSubWindow->setAttribute ( Qt::WA_DeleteOnClose );
mdiSubWindow->setWindowTitle ( fileinfo.absoluteFilePath() );
mdiSubWindow->showMaximized();
mdiSubWindow->setMinimumSize ( QSize ( 128, 128 ) );
window->setModel ( fileinfo.absoluteFilePath() );
}
}

The full code of the project is at:

https://github.com/AeonGames/AeonEngine/tree/master/tools/modelviewer

It is not exactly easy to build, but it may help to look at the code when root causing the issue, I may try to create a minimal test case if required. (I don't think OpenGL or Vulkan is the reason for the problem)

See images attached for visual aid.