Transparent QGraphicsProxyWidget Rendering Artifacts

We have an application that uses stylesheets to set the background color of widgets to be transparent before adding to QGraphicsProxyWidgets and a QGraphicsScene. This allows us to have semi-transparent windows moving around the canvas so that we can see what is behind them. Recently we have upgraded from 4.6.0 to 4.6.2 and we now see some rendering artifacts when caching the graphics items. It appears that the pixmap that we are caching into doesn't get completely cleared before re-drawing. Since the background is semi-transparent this results in rendering artifacts. I believe that I have tracked it down to a change [1] to the painter composition mode when rendering a subpixmap into the entire cached pixmap. I have been unable to find the correct bug to read more about what this commit fixed, but it seems that it might have broken our use case. I would think that since we are re-drawing a section of a cached item we would not have a need for blending. I have attached a simple example showing the issues we are seeing.

[1] http://qt.gitorious.org/+qt-s60-developers/qt/qt-s60/commit/39392326c8c843a6f46b864c6595a5241a47af10?diffmode=sidebyside