title: PyQt: QGraphicsItem added at a wrong position
body: <p>I have a subclass of QGraphicsItem and I want to add instances of it to the scene on 'Control+LMB click'. The trouble is that the item is added at the position with coordinates that are two times larger than they should be. At the same time adding ellipses with scene.addEllipse(...) works fine.</p>
  
  <pre><code>#!/usr/bin/env python
  
  import sys
  from PyQt4.QtCore import (QPointF, QRectF, Qt, )
  from PyQt4.QtGui import (QApplication, QMainWindow, QGraphicsItem, 
                           QGraphicsScene, QGraphicsView, QPen, QStyle)
  
  MapSize = (512, 512)
  
  class DraggableMark(QGraphicsItem):
      def __init__(self, position, scene):
          super(DraggableMark, self).__init__(None, scene)
          self.setFlags(QGraphicsItem.ItemIsSelectable | QGraphicsItem.ItemIsMovable)
          self.rect = QRectF(position.x(), position.y(), 15, 15)
          self.setPos(position)
          scene.clearSelection()
  
      def boundingRect(self):
          return self.rect
  
      def paint(self, painter, option, widget):
          pen = QPen(Qt.SolidLine)
          pen.setColor(Qt.black)
          pen.setWidth(1)
          if option.state &amp; QStyle.State_Selected:
              pen.setColor(Qt.blue)
          painter.setPen(pen)
          painter.drawEllipse(self.rect)
  
  
  class GraphicsScene(QGraphicsScene):
      def __init__(self, parent=None):
          super(GraphicsScene, self).__init__(parent)
          self.setSceneRect(0, 0, *MapSize)
  
      def mousePressEvent(self, event):
          super(GraphicsScene, self).mousePressEvent(event)
          if event.button() != Qt.LeftButton:
              return
  
          modifiers = QApplication.keyboardModifiers()
          pos = event.scenePos()
          if modifiers == Qt.ControlModifier:
              print("Control + Click: (%d, %d)" % (pos.x(), pos.y()))
              DraggableMark(pos, self)
              self.addEllipse(QRectF(pos.x(), pos.y(), 10, 10))
          else:
              print("Click: (%d, %d)" % (pos.x(), pos.y()))
  
  
  class MainWindow(QMainWindow):
      def __init__(self, parent=None):
          super(MainWindow, self).__init__(parent)
          self.scene = GraphicsScene(self)
          self.scene.addRect(QRectF(0, 0, *MapSize), Qt.red)
          self.view = QGraphicsView()
          self.view.setScene(self.scene)
          self.view.resize(self.scene.width(), self.scene.height())
          self.setCentralWidget(self.view)
  
  
  if __name__ == "__main__":
      app = QApplication(sys.argv)
      window = MainWindow()
      rect = QApplication.desktop().availableGeometry()
      window.resize(int(rect.width()), int(rect.height()))
      window.show()
      app.exec_()
  </code></pre>