The scene represents the base coordinate system for all its items. The scene coordinate system describes the position of each top-level item, and also forms the basis for all scene events delivered to the scene from the view

This is what QtAssistant says... what I understand there is that inside the same scene, there shouldn't be two items, in the same position, but in different position once they are displayed... I mean, the variable says they are in the same position but graphically they are in different places (and always inside the same scene).