Graphics effects that change the bounding rect don't work properly when nested

Given the following circumstances:

• QGraphicsItem r1, with a child QGraphicsItem r2
• r2 has a QGraphicsEffect which changes the boundingRect (e.g. drop-shadow)
• r1 has any QGraphicsEffect

The effect on r1 wouldn't take into account the new bounding rect that was generated by the effect on r2.
The test case shows it; If the opacity effect on r1 is enabled, the drop-shadow would go away, while if the opacity effect is disabled with the --shadow-only command line argument, the shadow is visible.