Release shift before left mouse button during rubberband mode does not erase rubberband

In a class that derives from qgraphicsview, override mousePressEvent(). In there, test for the shift modifier, and if so, turn on rubber-band dragging (setDragMode(rubberband)). In the mouseReleaseEvent, use setDragMode(dragcanvas). Now when you run the program, press the shift key and hold, click left mouse button and drag, holding the click; the rubber band appears and forms a rectangle based on where the mouse cursor is; now release the shift key, without releasing the left mouse button; the rubber band does NOT disappear. Note that if you release the left button before the shift, the rubber band does disappear. According to a reply to a post,

Technically I believe this is a bug caused by setDragMode not setting private d->rubberBanding = false; This is making paint to draw last set d->rubberBandRect even technically in the current selection or dragging mode such rfectangle should not be displayed. Unfortunately since problem is in a private inaccessible variables fixing a source of the problem seems impossible.

This issue is discussed in http://forum.qt.io/topic/64033/invalidatescene-problem/7.