QGraphicsItem paint is not being called

Hello everyone! I’m working on a project, where I use QGraphicsScene, QGraphicsViwe, QGraphicsItem. I’m drawing QGraphicsItems and the problem is that, although bounding rects are being calculated correctly QGraphicsItem::paint is not being called for all items. What can cause such problem? Why do QGraphicsItem::paint should be called for some items and for some items not? Thank you in advance!