QTreeView: painting custom QStyle::PE_FrameFocusRect leaves artifacts

The sample project (.zip file attached) creates a QTreeView and paints a custom focus frame (QStyle::PE_FrameFocusRect). Painting itself works, but it seems the items that go out of focus are not invalidated, hence visual artifacts of the focus frame are left behind. Hovering the mouse cursor over such an item causes a repaint and erases the leftovers. Here's what it looks like:

Observations:

1. Problem doesn't occur with pen size 0, does occur with anything larger than that.
2. Problem doesn't occur if painting a fillRect with a solid brush.