Please see attached example.

Parent (black rectangle) has 4 children (blue rectangles) and overloaded shape() method to return shape set by user.
Shape of the parent is set to circle and QGraphicsItem::ItemClipsChildrenToShape flag is set to true.
In this configuration children should be clipped to the shape defined, but parent should be entirely visible.
In Qt 4.5.2 it's the case but in Qt 4.6.0 and later parent gets clipped to the same shape as children.

Setting QGraphicsItem::ItemClipsToShape on parent to false doesn't change anything.