QGraphicsItem inconsistent collidingItems from paint

When calling collidingItems() from the paint method of QGraphicsItem, a distinct value is returned if the method call happens to be from the gui thread, or from scene()->render().

To use the testcase in attachment, first read the main.cpp and foo.cpp files, then run  "waf configure build" to run if deemed necessary. The only two graphics items collide with each other, so no "0" should be ever output to the console.

While changing the index method seems to be a workaround, it would be great to know why such an inconsistency is happening.

    scene.setItemIndexMethod(QGraphicsScene::NoIndex);

Also, if checking for collisions while painting is a bad idea, then a hint somewhere would be good to have too