Qslider inside qgraphicsview

[MAX1971]

HELLO,
I create inside a QGraphicsView a slider vertical bar adding it like QGraphicsProxyWidget.
I want that if the user move inside the view(moving scroll bar for example) is always visibile.

To do this i use SetPos inside paintEvent of my view.

But if the user move very fast the scroll bar i see the effect you can see in attachment, the slider is like paint in different position.

I'm wrong in something?

Thanks in advance