QGraphicsItem - Cache without clear

Customer says: "I have attached a stripped down test app which demonstrates the problem. In the app there is a single item which covers the entire screen. Initially it paints 100 rectangles, then in each future frame 25 of the rectangles change colour. Without the suggested modification only the rectangles painted each frame can be seen. However, if the clear in the qgraphicsscene ItemCoordinateCache code is commented out you would correctly see all 100 rectangles every frame with only the first 25 changing colour. Basically, if the clear is left in the graphics item is forced to repaint everything every frame. In this simple test app that may not be a huge issue but if the item consists of a lot of complex visuals it can be very expensive."