setCacheMode( CacheBackground ) causes the background to not repaint correctly

I'm attaching a code that shows a custom widget over a graphics view, it has the weird problem of

• You minimize the window
• You restore the window
• You click somewhere in the map 1 or 2 times, when you do it the third time
  there is a white rectangle where the information of the second country was.

This is reproducible with Qt 4.6 both in Linux and Windows
I'm attaching the code and a screenshot.

Removing setCacheMode( CacheBackground ) makes it work but obviously it's not what one wants