QLineEdit with a QCompleter: popup completion is drawn on the wrong location

If adding a QLineEdit to a QGraphicsScene as a QGraphicsProxyWidget, the popup completion of that QLineEdit is drawn in the wrong location. E.g. the QGraphicsProxyWidget/QLineEdit can be drawn in the center of the scene (pos = (0,0)), but the popup is drawn in the upper left corner of the main window. I therefor think that the mapping between the different coordinate systems (scene <-> main window) isn't working properly.

edit: attached a screenshot