Painting problem when QMdiSubWindow is moved over QGraphicsView

Hi,

I have a MainWindow class inside that I have GraphicsView. I am using a custom GraphicsScene in which drawBackground() and drawForegroud() functions are reimplemented.

Here is my code http://dpaste.com/hold/161434/

Problem : When I hover a QMdiSubWindow over GraphicsView, graphicsview doesn't get updated properly. In my program if I am commenting

painter->drawLine(rect.left()+20 , rect.top(), rect.left()+20, rect.bottom());
and using
painter->drawLine(20 , 20, 20, 600);
then there is no problem.

Thanks in advance.