It is possible to begin a drag & drop sequence using the forward/backward mouse buttons while moving the cursor.
For example:
QGraphicsSceneMouseEvent(GraphicsSceneMouseMove, buttons=ForwardButton|XButton2|ExtraButton2, pos=347,127, scenePos=347,127, screenPos=398,255)
This patch only allows drag & drop if the left mouse button is pressed.
Touch events should not be affected as they are handled separately.