QGraphicsScene update large rectangle when ListView scrolling

I scrolled on the ListView, and I noticed that the QGraphicsScene::update will take one or two large size rectangle up to draw on, and it got much pain on my embedded environment.

Why would we need to paint this large rectangle? It seems ok if I ignore this rectangle and draw remains by manual.

Scene update rects : (QRectF(0,0 1920x4427) ) --> this
Scene update rects : (QRectF(0,0 1920x4427) ) --> this
Scene update rects : (QRectF(835,418 250x4000) , QRectF(838,411 194x34) , QRectF(929,416 12x24) , QRectF(838,451 194x34) , QRectF(929,456 12x24) , QRectF(838,491 194x34) , QRectF(929,496 12x24) , QRectF(838,531 194x34) , QRectF(929,536 12x24) , QRectF(838,571 194x34) , QRectF(929,576 12x24) , QRectF(838,611 194x34) , QRectF(929,616 12x24) )