QGraphicsView rubberband selection

I'm using QGraphicsView with custom QGraphicsItems (which are currently just ellipses with overloaded boundingBox(), shape() and paint() methods). When dragMode is set to NoDrag simple selection works OK. But when dragMode is set to RubberBandDrag it sometimes misses my clicks (i.e. do not selects item when I single click on it) and Ctrl and Shift modifiers for selecting several items refuses to work. Rubberband selection (when I drag the mouse) works well.
Is it supposed behaviour or I'm doing something wrong ?

I can't be certain, but this behaviour seems logical.

Can you reproduce this problem with the Qt demo app? It uses rubber band dragging with item selection. It is also used as a manual test bed for item selection, and seems to work as designed.